Ultra High Temperature Ceramics for Thermal Protection

Ultra High Temperature Ceramics for Thermal Protection Recent Developments in Oxidation Resistance and Fracture Toughness of Ultra High Temperature Ceramics for Thermal Protection Systems Katrin Abrahams (Dated: February 3, 2015) For safer and faster space vehicles a reduction of the tipradius of the leading edges is inevitable. This leads to temperatures exceeding 2200  °C which the used material has to withstand. ZrB2/SiC and HfB2/SiC have suitable properties, but the oxidation resistance and fracture toughness at high temperatures have to be improved. This review describes the recent approaches to handle these problems that base mainly on the addition of a third material (La2O3, Gd2O3 or graphite). The addition of either La2O3 or Gd2O3 led to increased oxidation resistance, but the processing, the amount of additive and the testing methods have to be improved. Due to the addition of graphite à ¯Ã‚ ¬Ã¢â‚¬Å¡akes the fracture toughness of ZrB2/SiC (20 vol%) increased from 1. INTRODUCTION The Thermal Protection System (TPS) of space ve ­hicles is one of the most important parts of the whole vehicle [1–3]. This protects it from the heating during re-entry. During this process the temperatures are very high, especially at the nose cone and leading edges as shown in Fig. 1. Figure 1: Temperature proà ¯Ã‚ ¬Ã‚ le of a space vehicle during re ­entry prepared by the NASA. The dark red colour represents the highest temperatures and the light blue regions are coolest parts (copied from [4]). The tip of the leading edge has a radius of 10 cm, but a radius in the range of millimetres is wished so that sharp leading edges instead of blunt leading edges can be used [5]. This would have the advantage to â€Å"help reduce the vehicles drag, enhance maneuverability and performance, and also improve safety due to an increased cross-range-capability† [5]. The problem of a smaller tip radius is that this leads to higher surface temperatures, which can exceed 2000  °C [6, 7]. Jin et al. [8] investigated the maximum surface tempera ­ture depending on the radius of the tip using an oxyacety ­lene torch. Fig. 2 shows that the temperature increases from 1930  °C with a radius of 1.5 mm to 2100  °C with the radius of 0.15 mm. Due to the high requirements for these materials only a few can be considered. Very good potential for the usage show Ultra high temperature ceramics (UHTC). These are ceramic materials with high melting points (> 3000  °C), good thermal shock resistance and chem ­ical and mechanical stability e.g. ZrB2, ZrC, HfB2 or HfC [6, 9, 10]. Although the carbides have a higher melt ­ing point than the diborides, their thermal conductivity is lower, which is very important because the heat on the surface has to be transported as fast as possible away [5]. Therefore the main focus of research is on ZrB2 and HfB2. The problem with these diborides is their brittleness and their oxidation at temperatures exceeding 1200  °C [11]. To fabricate a more ductile material SiC was added to ZrB2 or HfB2 [12]. Although ZrB2/SiC and HfB2/SiC are promising materi ­als for the usage in TPS, there are still two main problems which have to be solved. On the one hand side there is still the problem with the oxidation resistance at higher temperatures [11, 13]. On the other hand the fracture toughness decreases with the temperature to rather low values which also leads to mechanical problems [14]. This review gives an overview over solution attempts that have been made in the last years, with the main focus on ZrB2/SiC. 2. OXIDATION RESISTANCE The oxidation resistance of MeB2/SiC (Me = Zr, Hf) depends on the ratio of MeB2/SiC [10, 15], the pres ­sure [10, 16, 17], the temperature [18], the exposure time [19], on the processing [20, 21] and in case of the addition of additives also on their chemical structure and the amount of additive [22, 23]. Considering just ZrB2, the following happens during ox ­idation [24]: The liquid B2O3 forms a protection layer for the porous ZrO2 layer, where oxygen can dià ¯Ã‚ ¬Ã¢â€š ¬use very fast and easily through. But at 1100  °C this protective layer evaporates and cannot prevent the oxidation of the bulk material anymore. The addition of SiC leads to the following additional re ­actions [10, 25, 26]: During oxidation four dià ¯Ã‚ ¬Ã¢â€š ¬erent layers can form (Fig. 3). Above the bulk material the SiC depleted zone forms, where SiC oxidizes to SiO2 which forms a borosilicate (BS) glass on the surface. This layer is porous due to the formation and evaporation of CO (Eq. (2)). Above this layer there is the oxidized layer, which consists of porous ZrO2 and the upper layer is the Silica rich layer which consist of the BS glass, that also à ¯Ã‚ ¬Ã‚ lls partly the pores of the ZrO2 layer. Due to the evaporation of B2O3, the protection layer is shrinking over time and shows an oxidation resistance up to 1600  °C [24, 26]. In general the oxidation resistance is measured by the thickness of the reaction zone under the given parameters of the experiment. But also the dià ¯Ã‚ ¬Ã¢â€š ¬usion coeà ¯Ã‚ ¬Ã†â€™cient of O2 is important but rarely measured. 2.1. Ratio ZrB2/SiC The dependency of the oxidation resistance on the ra ­tio of ZrB2/SiC was investigated by many researchers [10, 12, 15, 27–29]. The addition of SiC led in all cases to a re ­duction in grain size, a homogeneous distribution of SiC, higher viscosity and higher density. Karlsdottir et al. [29] investigated not only the reaction Figure 3: Schematic demonstration of the dià ¯Ã‚ ¬Ã¢â€š ¬erent layers that form during oxidation of ZrB2/SiC and their arrangement. zone thickness but also the viscosity depending on the volume fraction of SiC. The results are shown in Table I and an increase in viscosity with the amount of SiC can be seen. This reduces the dià ¯Ã‚ ¬Ã¢â€š ¬usion coeà ¯Ã‚ ¬Ã†â€™cient of O2 in the layer. Seong et al. [10] compared ZrB2, ZrB2/SiC (20 vol%), ZrB2/SiC (30 vol%) and ZrB2/SiC (40 vol%) and mea ­sured the resulting thickness of the reaction zone. All samples were densià ¯Ã‚ ¬Ã‚ ed by hot pressing and exhibit a ho ­mogeneous distribution of SiC. The grain sizes were be ­tween 1.0  µm and 3.0  µm. They investigated the oxi ­dation under low and high pressure and the results are shown in Figure 4. The SiC depletion layer did not form and therefore the reaction zone consisted only of the Silica rich layer and the oxidized zone. In air (2âˆâ€"104 Pa) the thickness of the reaction zone was in ZrB2 the thickest due to the missing protecting silica layer and with increasing amount of SiC the thickness de ­creases. The problem with high amounts of SiC (30 vol%) is, that it does not form single grains anymore, but in ­stead a network, which leads to higher porosity. Under low pressure the behaviour is vice versa. Because the space shuttle has to deal with low and normal pressure ZrB2/SiC with 20 vol% or 30 vol% SiC is the best choice. Apart from the improvements of oxidation resistance due to optimization of the ZrB2/SiC ratio, at temper ­atures above 1800  °C active oxidation (Eq. (4)) of SiC takes place and this hinders the formation of the BS layer. 2.2. Additives To increase the oxidation resistance at higher temper ­atures transition metals were added to the ZrB2/SiC ma ­trix [21, 30–32]. They are suitable due to their high melt ­ing points and low reactivity with the environment [30]. The transition metal cations can be enclosed in the BS layer to form a higher viscous layer that decreases O2 dià ¯Ã‚ ¬Ã¢â€š ¬usion [11]. Furthermore this may lead to a higher evaporation point of the protective layer so that the ma ­terials are stable at T > 2000  °C. This is based on an assumption, the mechanism how the transition cations interact with ZrB2 and SiC is not understood yet but in general a positive trend to higher oxidation resistance can be seen [11]. Several attempts were made with many dià ¯Ã‚ ¬Ã¢â€š ¬erent transi ­tion metal oxides [9, 30], borides [11, 33], carbides [21, 31] and silicates [32]. This review focuses on La2O3 and Gd2O3 because they are the most promising additives and introduce two dià ¯Ã‚ ¬Ã¢â€š ¬erent processing methods that ef ­fect the properties [30]. 2.2.1. Addition of La2O3 The addition of La2O3 to ZrB2/SiC was investigated by several researchers and led to dià ¯Ã‚ ¬Ã¢â€š ¬erent results, espe ­cially various new phases were found [6, 9, 22, 23]. Ta ­ble II gives an overview over the composition, the pro ­cessing routes to densify the material and the new phases that were discovered. Although Table II shows many dià ¯Ã‚ ¬Ã¢â€š ¬erent results, gen ­eral trends due to the addition of La2O3 despite the usage of dià ¯Ã‚ ¬Ã¢â€š ¬erent processing routes (hot pressing, spark plasma sintering (SPS)) were observed [6, 22, 23]: †¢ Higher density Higher Vickers Hardness Reduction of grain sizes Besides the use of La2O3 leads to a more homogenized distribution of SiC, because it is always close to it and therefore prevents agglomeration [9]. In the case of fracture toughness there are contradictory statements: Li et al. [22] measured an increased fracture toughness compared to the material without additive and Guo et al. [23] published a lower fracture toughness due to the addition of La2O3. After hot pressing at 1900  °C for 60 min Li et al. [22] dis ­covered the formation of new phases: La2Zr2O7 (melting point: 2295  ± 10  °C [9]) and La2Si2O7 due to the follow ­ing reactions: 2ZrO2(s)+ La2O3(s) → La2Zr2O7(s) (5) 2SiO2(s)+ La2O3(s) → La2Si2O7(s) (6) La2Zr2O7 was also observed by Zapata et al. [6] and Jayaseelan et al. [9] but no other working group detected the formation of La2Si2O7. The addition of 10 wt% La2O3, densià ¯Ã‚ ¬Ã‚ ed by SPS and oxidized for 1 h in air at 1600  °C led to the formation of two dià ¯Ã‚ ¬Ã¢â€š ¬erent oxidized layers [9]. On the surface a La ­BS-glass formed (Eq. (7)), below it two oxidized layers, one consisting of La2Zr2O7 (Eq. (5)) and the other one of ZrO2. SiO2 + La2O3 → La − BS − glass (7) The large expansion coeà ¯Ã‚ ¬Ã†â€™cient of La2O3 causes à ¯Ã‚ ¬Ã‚ lling of the pores that appear after the evaporation of B2O3 and therefore still protects the bulk material. The same composition and the same processing was used by Guo et al. [23] but they could not detect the new phases. Instead they found out that La2O3 reacts Table II: Overview over the composition (always ZrB2/SiC (20 vol%) + the given amount La2O3), the processing route and the new phases that formed. amount La2O3 processing new phase 5 vol% hot pressing La2Zr2O7 (1900  °C, 60 min) La2Si2O7 3 vol% hot pressing La2O3-SiO2 (1900  °C, 60 min) 10 wt% SPS La2Zr2O7 oxidized (1600  °C, 1 h, air) La-BS-glass 2 wt% SPS La2Zr2O7 oxidized (1400  °C, 16 h, air) La-BS-glass with SiO2 to form La2O3-SiO2 as a protective layer. Further studies were made by Zapata et al. [6] who used less La2O3 (2 wt%). Due to the proximity of the La2O3 particles to the SiC particles they are also included in the BS melt whereby this results in a higher viscosity, a higher thermal stability and in general a better protec ­tion against O2 dià ¯Ã‚ ¬Ã¢â€š ¬usion. The oxidation tests show that at 1400  °C the sample with La2O3 has a better oxidation resistance but at 1500  °C and 1600  °C it is worse. The reason is that because of the addition of La2O3 the BS layer has a higher viscos ­ity and therefore the ZrO2 particles cannot precipitate directly to the top of the surface layer. This leads to a more homogeneous mixing with the BS melt. The oxy ­gen dià ¯Ã‚ ¬Ã¢â€š ¬usion through ZrO2 is much easier than through B2O3 and therefore a homogeneous distribution of ZrO2 makes it easier for O2 to dià ¯Ã‚ ¬Ã¢â€š ¬use through this layer, al ­though the La-BS-glass has a higher viscosity due to the addition of La2O3. Mo reover at 1600  °C ZrOxCy and SiOxCy form with dif ­ferent O/C ratios which were found in the BS melt and in the oxide layer [6]. This can be seen as another pro ­tection layer because when O2 dià ¯Ã‚ ¬Ã¢â€š ¬uses into the oxidation layer it will react with ZrOxCy or SiOxCy, so it can be seen as a puà ¯Ã‚ ¬Ã¢â€š ¬er zone and it takes longer until the oxygen reaches the bulk material. HfB2 dià ¯Ã‚ ¬Ã¢â€š ¬ers from ZrB2 because the formation of HfO2 is more dià ¯Ã‚ ¬Ã†â€™cult [6]. Therefore a smaller amount is formed which leads to a lower amount of B2O3 and therefore a thinner protection layer compared to ZrB2. But it has the advantage that the dià ¯Ã‚ ¬Ã¢â€š ¬usion coeà ¯Ã‚ ¬Ã†â€™cient for O2 through HfO2 is smaller. Another problem in the case of HfB2 is that SiC is not as homogeneously distributed as in ZrB2 and it forms large agglomerates. When these agglomerates become oxidized they leave behind a highly porous material where O2 can easily dià ¯Ã‚ ¬Ã¢â€š ¬use throug h. This shows that further improvements are inevitable in a more homogeneous distribution, further analysis of the new formed phases must be made and the C/O ratio can Figure 5: Topview (a) and sideview (b) of the surface with the dimensions of the cavities for Gd2O3. oxidation layer was 15  ± 3  µm and formed in accordance with the following reaction equation [9]: 2Gd2O3(s)+2ZrO2(s) → Gd2Zr2O7(s) (8) Gd2O3(s)+ SiO2(s)+ B2O3(l) → Gd − BS − glass (9) The thickness of the layer below it was 160  µm and consisted mainly of porous ZrO2 due to the oxidation and evaporation of the glassy phase. The advantage of Gd-BS-glass compared to BS glass is the higher viscosity and therefore the reduced dià ¯Ã‚ ¬Ã¢â€š ¬usion of O2 through this coating. At higher Gd2O3 fractions Gd stops ZrO2 particles at the glassy phase and they cannot dià ¯Ã‚ ¬Ã¢â€š ¬use further. This leads to O2 vacancies which is the driving force for inward O2 dià ¯Ã‚ ¬Ã¢â€š ¬usion. Using a distance of 20  µm between the cavi ­ties, the Gd2O3 fraction is high enough to get a higher viscosity in the BS melt but ZrO2 can still precipitate so that no O2 inward dià ¯Ã‚ ¬Ã¢â€š ¬usion occurs. 3. FRACTURE TOUGHNESS In 2009 the à ¯Ã‚ ¬Ã‚ rst tests were made to include graphite in the ZrB2/SiC matrix [34, 35]. Hu et al. [34] investigated the fraction of additive graphite to ZrB2/SiC (20 vol%). They found out that the addition of graphite led to a 1high dense material with an increasing fracture toughness be optimized. But the addition of La2O3 is already a from 4.5 MPam (ZrB2 + SiC (20 vol%)) to 6.1 MPam1 22 very promising approach for a better oxidation resistance although further research is necessary. 2.2.2. Addition of Gd2O3 For an improved surface and at the same time un ­changed bulk material a new processing method was in ­vented [11]: At à ¯Ã‚ ¬Ã‚ rst the sample was prepared and densi ­Ãƒ ¯Ã‚ ¬Ã‚ ed using the bulk material ZrB2/SiC. Afterwards they used a laser to make equal sized cavities on the surface that were à ¯Ã‚ ¬Ã‚ lled with Gd2O3 nanopowder. The dimen ­sions of the best sample can be seen in Fig. 5. Due to this new processing it was possible to create only a thin protection layer that consisted of BS mixed with Gd2O3 ( Eq. (9)). After 1 h in air under 1600  °C the thickness of the outer (ZrB2 + SiC (20 vol% + graphite)). The dià ¯Ã‚ ¬Ã¢â€š ¬erences be ­tween 10 vol% and 15 vol% graphite were negligible small. Moreover there were investigations about the inà ¯Ã‚ ¬Ã¢â‚¬Å¡uence of the diameter size of the graphite à ¯Ã‚ ¬Ã¢â‚¬Å¡akes [36]. They found out that in the range of micrometres the diameter size does not change the fracture toughness. Asl et al. [14] used soft graphite nano-à ¯Ã‚ ¬Ã¢â‚¬Å¡akes. They found out that ZrB2 + SiC (20 vol%) + graphite (10 vol%) showed a higher density than the samples without graphite. Furthermore the addition of graphite led to a decrease in grain size from 6.9  µm to 3.2  µm. The reason is the homogeneous distribution of graphite which stopped grain growth. Because of the reactions of graphite with the surface impurities the addition of graphite results in higher dense samples: ZrO2(s)+ B2O3(l)+5C(s) → ZrB2(s)+5CO(g) (10) The particles that form due to this reactions can à ¯Ã‚ ¬Ã‚ ll the pores in the ZrB2/SiC matrix and therefore lead to a higher density. The resulting fracture toughness can be seen in Fig. 6. An increase in fracture toughness due to the addition of graphite is obvious. The following mechanisms led in this case to a higher fracture toughness: nano-à ¯Ã‚ ¬Ã¢â‚¬Å¡akes pull-out, crack bridging, branching and deà ¯Ã‚ ¬Ã¢â‚¬Å¡ection. 1 Figure 6: Fracture toughness depending on the composition of the sample at RT [14]. Wang et al. [37] investigated the dependency of the fracture toughness of ZrB2 + SiC (20 vol%) + 1 graphite (15 vol%) on the temperature in vacuum and in air (Fig. 7). Over the whole temperature range the fracture toughness in air was higher than that in vac ­uum. In vacuum the fracture toughness decreases from This oxidation layer densià ¯Ã‚ ¬Ã‚ es with higher tempera ­ture and yields in higher fracture toughnesses than with ­out this layer. That is the reason why there is nearly no decrease in fracture toughness between 1200  °C and 1300  °C. Moreover crack deà ¯Ã‚ ¬Ã¢â‚¬Å¡ection which absorbs the energy leads to higher fracture toughnesses at higher temperature. These mechanisms all result in a slower decrease in frac ­ture toughness in air than in vacuum. Figure 7: Fracture toughness depending on the environment and on the temperature [37]. 4. CONCLUSION The recent developments to improve the oxidation re ­sistance and the fracture toughness based mainly on the addition of a third component (La2O3, Gd2O3 or graphite). Concerning the oxidation resistance, the best matrix composition is ZrB2/SiC (20 vol%) because it shows the best oxidation protection over the whole range of O2 partial pressure. Above 1800  °C active oxidation of SiC begins and oxidation resistance is not given anymore. at 1300  °C because The approaches for a better oxidation resistance at higher ual thermal stresses between the ZrB2/SiC matrix and temperatures due to the addition of La2O3 or Gd2O3 arethe graphite inclusions are released. The residual stresses very promising, but more research to understand the real acted at low temperature as toughening mechanism and function of the additives and the interaction with the ma ­with the release of these stresses the fracture toughness trix is necessary. Furthermore there are many parameecreases. At 1300  °C the group observed a brittle to ductile trans ­formation which leads to a slight increase of fracture toughness. But afterwards the fracture toughness de ­creases further due to the distorted graphite and the larger ZrB2 grain sizes. In air at higher temperature the material starts to ox ­idize and a oxidation layer forms on the surface due to ters that have to be optimized, e.g the amount of ad ­ditive, the processing route and especially the analytical approaches. Due to the varying experimental parameters and insuà ¯Ã‚ ¬Ã†â€™cient analytical tests it is dià ¯Ã‚ ¬Ã†â€™cult to compare results. To solve this problems standard tests have to be introduced and a wider temperature range for oxidation has to be investigated. The fracture toughness increased due to the addition of Eq. (1), (2) and the following reaction: graphite from 4.5 MPam to 7.1 MPam creases, but also this is slowed down due to the graphite tives, because extensive testing of the dià ¯Ã‚ ¬Ã¢â€š ¬erent samples à ¯Ã‚ ¬Ã¢â‚¬Å¡akes. is missing. Especially tests under real atmospheric and Taken into account the oxidation resistance and the frac-re-entry conditions are important but not done yet. ture toughness it is dià ¯Ã‚ ¬Ã†â€™cult to announce the best addi ­

Kerrang Magazine Blink182 Article Analysis :: Papers

Kerrang Magazine Blink182 Article Analysis * Blink182 - when they were younger * This Blink182 interview was published in alternative music magazine 'Kerrang' - issue 979 in November and was written by Tom Bryant. It's purposes are mainly to discuss their past, their success and above all their new album ! They tell us how it was almost never made as two years ago they were ready to split. This article is informative and at times quite humorous, 'There are many ways you'd imagine how a conversation with Tom DeLonge might start. Most of them involve a certain level of immaturity, a teenage crack about blow jobs, poop or possibly your mother. A reasoned debate on Californian politics is roughly last on the list '. But it also feels sad as the band recall feeling as though they were drifting apart. I think fans of the band would find this piece interesting. The implied readers would include Blink's fans (usually teenagers), people considering buying their latest album, fans of punk-rock music and people who may just be curious about them. So in general - most readers of 'Kerrang' i.e- people interested in alternative music such as punk, metal and rock. Having read the article through a few times now i have noticed that it differs to previous Blink interviews i have read. As a group they have been out of the public eye for the past two years producing their self titled album. Although Blink are a hugely successful, international band and every young person knows a little about them i dont think there is any evidence of implied reader knowledge. After reading the title page 'But seriously folks...' we know right away Blink have grown up as it describes their old stuff is out and new mature material is the way forward. This feeling of change continues throughout the piece. It feels new, exciting and deep. I dont think this interview was planned, as the guys seem to be relaxed and speak their mind. Which i think helps put their

Effects of Smoking While Pregnant :: smoking while pregnant

During a pregnancy there are many choices to be made and smoking should not be one of them. Smoking while pregnant can cause major effects before the birth of the child and also in the child’s future. Here are a few effects before the actual birth of the child: 1) Cigarettes contains a large number of chemicals that harm unborn babies. 2) Smoking raises the levels of carbon monoxide in your bloodstream. This gives less oxygen for baby. 3) Nicotine tightens the blood vessels, meaning the oxygen is passed over less effectively to the baby 4) Miscarriage or stillborn.   Ã‚  Ã‚  Ã‚  Ã‚  The risk of Sudden Infant Death Syndrome triples if the mother has smoked during pregnancy. â€Å"It is estimated that twenty-five percent of expectant mothers in the U.S. smoke throughout their pregnancies. According to a report from the Surgeon General, twenty percent of low birth weight births, either percent of preterm deliveries and five percent of all perinatal could be prevented by eliminating smoking during pregnancy.†   Ã‚  Ã‚  Ã‚  Ã‚  Not only can smoking cause considerable damage to the unborn baby, but it could affect the baby later in life. Smoking increases the chances of the baby having birth defects. For example, the child might develop severe brain damage. The baby also might be considerably light in weight. All these outcomes are extremely negative and can cause guilt.   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Another thing that should be taken into consideration is secondhand smoke. Even though the smoking is not being done firsthand, there is still a big risk. Side effects of secondhand smoke are ear infections, colds, and damage to the lungs. And even though it is not definite that complications during pregnancy might not occur, the chance of putting a child at risk for the sake of smoking a cigarette should not be taken.

The Effects of Addicting to Cyber Social Networks

The Effects of Addicting to Cyber Social Networks Social network is an addictive thing nowadays. I believe that everyone, start from teenagers up to old people addict to cyber social networks. Almost every single breathe, they update their twit, their statues, etc. If we cannot control ourselves to use this social network in the good way, it will not take a long time for us to get the bad impacts. There are so many bad impacts of addicting social networks.First of all, we will next to our far away people we usually connected to, but we will be far with the people around us. How come? Many people always keep contact to their friends in cyber world by social networking, so they often don’t care with the people around them. That condition absolutely makes others feel uncomfort to talk with that person. So, don’t be surprised if those real friends will stay away from that person. Actually it’s good to keep contact with people who far away with us. However, real frien ds are more important than cyber friends.Why? Because if we have a problem, real friends will help us directly than cyber friends. So the main point here, we have to priority our real friends first, then our cyber friends. The second is our main activity will be annoyed because of addicting to social networks. I am sure that we often meet someone who cannot live faraway from their gadget just to update his social networks. Don’t you ever think that this habit actually is annoyed his main activity? For example, there is a student in a class.All of us know that his main activity should be related with studying. However, if he is too busy with his social networks, how about his study? I believe that he will not be able to focus on his study because every single breathe he updates his social networks as I said before. That habit will also influence his score, how come? Because if we cannot focus on what we do, of course we will not be able to do it well. We will not be able to gi ve our best on it. The last but not least, addicting to social networks will give bad impact for our body.As we know that if we addict to something, in this case social networks, we will not be able to be separated with our gadgets. Whenever and wherever we go, those gadgets will stick with our hand, and absolutely it’s dangerous for us. Medical research has found that two mobile phones which are calling to each other for some hours can make an egg cooked. From that news, I think we should know how dangerous the radiation of this gadget is. Besides the radiation, too much doing this activity will make us feel lazy to move, we will sit all day long.Sitting for a long time is also not good for our body, we have to do exercise at least 15 minutes per day regularly. As you know, it is really dangerous for us if we cannot use cyber social networks in a good way. Being far away with people around us, annoying our main activity and also causing harm for our health is just some examp les of this bad habit. In my opinion, technology is good for us, but we have to use it in a good way too, so we can get the advantages. Sonia Dwi Cahyanti 110221414604/AA

Xerxes

Xerxes hand Prosecution Building Programs * Economic bloodline was related to his excessive building programs. * scour though his building programs were impressive he neglected other parts of the empire. * Olmstead Xerxes was much interested in completing the smart as a whip structures begun by his father than he was in testing the formidable war machine machine. * Josef Wieshofer Persepolis was one of his favourite past times, was barely independent of Darius style, was an imitation of standards. * Xerxes spent coarse time, energy and resources on massive edifice programs. granger Fo prevail Policy * ill to expand into Greece was a lack of military ability. * He sent a squadron of ships to give up the channel before Salamis which resulted in the take place being unmake. * Battle of Salamis lack of truth within his navy and land troops. * no matter of how big and revolutionary the military was, Xerxes shut up failed. * Didnt actually get involved, sit and watche d. Religious Policy * Sacrilege destroyed temples (Egypt and Babylon), melted down the statue of boron Marduk. Xerxes was a apparitional fanatic who deviated from the religious gross profit of his predecessorshe has become a icon for religious bigotry, fanatically interfering in sacred matters where his predecessors had kept a distance. Granger * Wasnt a pragmatic religious ruler killed priests, took their land, melted down the statue of Bel Marduk resulted in the discontinuation of the New forms Festival. * Babylonian people resented the reign of Xerxes and did non consider him their king and archaeologic evidence after this incident, Xerxes ceased calling himself the major power of Babylon.Relationships * Werent strong with the aristocracy was kill by a member of his nobility Character * Various ancient sources shoot him with impetuosity, arrogance, sadism, madness and gulibilty. * small, blubbering, ruled by women and eunuchs, inhuman in victory, spineless in defeat . classic propaganda * deeply flawed ruler, one to cost passion rather than reason. William Culican and Augustine Alletz Comparison to separate Kings * The classics liked to compare Xerxes with other Iranian kings to highlight his faults.In their comparison with Darius and Cyrus, Xerxes is hardly the paladin among kings as he is named in Persian inscriptions. Rather, he is the bad king, the ruthless despot, not at all in the usance of the good and just Persian kings of the past. * Xenophon Describes Cyrus as modest, tolerant and wise and the hero of Persia. Whereas Xerxes is interpret as an ambitious, often cruel and magisterial Oriental ruler, described as a courtly womaniser, concerned only with Persian expansion and greatness. Concluding Statement Greek sources agree on his bad rule, as yet though they are bias, this viewpoint is support up by Roman and forward-looking sources. * Rodgers as Xerxes had failed in war and in civil organization so likewise did Xerxes fail to surpass his great predecessor. * His megalomaniac motives, his move to master nature and ignore the gods, the sacrilegious destruction of foreign temples, his apparent stale disregard for the lives of his men and his mutilation of Leonidas body, together with his mania of luxury.

Radical Feminism Versus Liberal Feminism

Feminist theories atomic number 18 an offstage of wo custodys liberation faecal matter into nonional and philosophical discourse. They aim at understanding of the character of cozy activity in twinity . They in turn psychoanalyse womens genial roles and life experiences . While in general some provide a evaluate of social relationships . Most womens rightist theories also counseling on analysing sexual urge in comparability and the promotion of womens rights, interests and issues . Among much(prenominal)(prenominal) theories are the Liberal womens lib and the stalk womens liberation movement theories.While Liberal and ascendant womens liberation movement some(prenominal) seek to ensure that women suck in entrance money to resources and human rights in a gender pertain environment they however do non inescapably employ similar methods in achieving these results. Each has its induce distinct reason behind whatever methods they pack to get hold of their goals . Wikipedia the free internet dictionary defines feminism as the belief that women have equal political sympathiesal, social, and sexual, interlectual and frugal rights as men do. It a discourse that involves unlike movements, theories and philosophies which are concerned with the issues of gender differences .The adaptation of the equality for women and the campaign for womens rights and interests. Ritzer (1992) indentifies feminism as that bestride of theories which analyse the social world of the point of views of women and some former(a) minority homeifys and the major objective is to investigate the situations and experience of women in diverse societies. Britannica encyclopaedia indentifies the term feminism as used to describe a political or economic, cultural, or economic movement aimed at establishing equal rights and legal protection for women. It involves political, cultural sociological theories .As well as philosophises concerned with issues of gender difference s. It also is a movement that advocates for womens rights and interests. patriarchate according to Robert (1991) is derived from a Greek word Patria manner father and arche means to rule, beginning, and origins. A ph altogetheric coping of the family excising autocratic authority or by extension a member of the ruling class, brass of a beau monde controlled by senior men. Scafer (2000) describes a constitutional group as a group that is bound apart from otherwises be exploit of obvious physical differences. check to Bryson in Haralambos and Holborn (2000), understructure feminism is a hypothesis that views women as an oppressed group which has to struggle for its liberation against its oppressors. accord to Harton and Hunt , a patient of is one who accepts the social corpse of rules as basically sound solely feels that extensive reforms maybe needed. Liberal feminism is the scratch line form of feminism recorded it asserts the equality of men and women, done poli tical and legal reform. Its in the main individualistic thus it focuses mainly on womens ability to show and maintain their equality through their own action and choices .It looks closely at the interactions that lead amid men and women in the public welkin . Liberal feminism cites such interactions as the beginning ground from where to transform company into a more(prenominal) gender equitable place . However other issues important to liberal womens liberationists also include productive rights , abortion admission charge, sexual harassment voting , statement , fair compensation for croak , affordable health care , and bringing to light the frequency of sexual and domestic abuse against women. This philosophy tends to have a neutral vision towards different gender.It requires women to mould themselves to fulfill a citizenship that already exists. On the other draw essential feminism is a movement that got its intake largely from the Marxist theory. It addresses is sues Liberal feminism everyplacelooked. It is a current within feminism that pays a not bad(p) take of trouble to the theory of patriarchate. concord to Haralambos, Horlborn and Heald (2000), innate feminism blames the exploitation of women on men. The term Radical is derived from the Latin word Radix, radic, meaning the root.Radical feminist strongly count that the root cause of the heaviness of women emanates from the patriarchal society that they exist in. The main perpetrators universe male. They identify patriarch as a brass of strength that organises society into a complex of relationships establish on an assumption of males universe the more weapons-grade of the sexes. The end result in such societies is the heaviness of women by men . Radical feminists identify just one solution, to dispute and solely over sling patriarchy by whatever means possible . Including debate standard gender roles. Whatever they see as male subjugation of women calls for a reorder ing of society, Wikipedia the internet free dictionary. Liberal feminists generally work for the eradication of installational bias and the implication of snap off laws. They legally challenge ideas and practices that result in women being seen as second class citizens. They do not challenge capitalism, patriarchy or any other fundamental structures of society. They a dvocate for transformational changes. Liberal feminists wish to progress to gender equality by working with the system rather than over throwing it , or ensample liberals do not call for the abolishment of the marriage institution instead they want the institution to be unified in such a way that it is not oppressive and imbalanced . In demarcation line Radicals are extremists and they strongly moot in a subversive change. Radicals on the left wing according to Henslin (1995) believe that subjugation of women is the most basic and fundamental cause of oppression. Radicals therefore believe that the only way to deal with that oppression is to have a complete etymon change .They unlike the liberals, they call for the eradication of the actual structures that result in women being oppressed. Campbell and Warsaw (1970) ask that total feminism aims to challenge and over throw patriarchy, opposing gender roles and what they identify as male oppression of women. Liberal feminist movement is best-loved by government than other forms of feminism movements. The liberals see value in working with the system therefore usually the liberal feminists work spate in ease up with the governments.For example in the unify States of America Liberal Feminism have historically worked for the ratification of the Equal Rights Amendment which ensures that men and women are enured as equals under democratic laws that also make important subject fields of womens lives including reproduction, work and equal pay. In Britain they supported such measures as the Sex secretion Act (1975) and the Equal Pay Act ( 1970) in the hope that these would help end discrimination. Were as radical feminists dont work closely with the government and neither does the government desire to work with them.To them the government also represents within it patriarch. At the same(p) clip the government views the radicals more often than not inapplicable as they advocate certain changes that do not necessarily work hap in hand with what the government desires. Most times conflict occurs among the two. Radical feminism places emphasis on the oppression of women by men . This idea distinguishes the Radical theory from the Liberal theory as the later concentrates on the oppression of two men and women.Unlike the radical feminists, liberal feminist take into consideration little dominant men who are oppressed by other men. Thus liberals view gender disparity as power that men have as a group over women and also the power that some men have over women. According to Valerie Bryson (1999) radical feminists see women as an oppressed group who had to struggle for their own liberation. Radical feminists view society and especially the society and especially the family as the expose institution oppresses women in modern society. Similarly, liberal feminist also believe that the social system catalyses gender inequality.They believe that society should not impose break down roles for women and those they should be allowed to compete freely with men and they should make merry the same privileges and opportunities. Radical feminists challenge and thrive to completely over throw patriarchy, by opposing the modal(prenominal) gender roles. They believe that male domination over women is as a result of gendered roles. Such roles have a diminishing effect on the splendour of women is society. They argue that men exploit women because of the free domestic labour that they provide.Women are excluded from other important issues such as political sympathies and positions of power and influence. On the same note liberal feminists identify gender roles as one of the main reasons responsible for gender inequality. They believe that childhood conditioning prepares the children for the inflexible and rigid gender roles that they take up in the future. Valarie Bryson (1999) identifies Radical feminism, it tends to dissolve variations in experience of oppression of women of different classes and heathen background. Radical feminism originated from the west.Most radicals are fresh hence radical feminism tends to concentrate on those problems that affected the white women. Very little attention is paid to those that affected the black women. Similarly, liberal feminism originates from the western hemi flying field hence most who tolerate to this school of thought are white women . According to Giddens (2004), liberal feminists aim for gradual change in the political, economic and social systems of western societies. Therefore liberal feminism too tends to ignore the experiences o f women in other societies.The liberal feminists have played a gigantic rule in ensuring that women in Zimbabwe have access to resources and opportunities . They set up organisations that see to the welfare of women. For example the Musasa Project. This project aids mostly women who would have been subjected to furiousness and the aid is for free. It has assisted women to come to terms with issues such as physical abuse by spo uses and boyfriends as well as to help them realise that it is not right them to be abused in such ways.Likewise radical feminists have fought for women to have equal access as men to resources. Through doing so several groups have been formed by the Radical feminists in Zimbabwe organisations such as WOZA and Girl Child. WOZA, Women of Zimbabwe scrape is an organisation that was started in 2003 by women who felt compelled to charge female voices in Zimbabwe. Their main objective was to achieve social justice for women as well as to provide them with a for um on which they could deliver about the things they want for their country.In conclusion both liberal and radical feminism provide women all over the world with a platform to piece their experiences. They both involve the formation of organisations that provide a voice for women to be heard. While Liberal feminists challenge only ideas and practises that treat women as second class citizens. They concentrate mostly on the public sphere issues, for example representation off women in politics and women being paid equal salaries with men when acting similar jobs.While on the other hand the radical feminists challenge the private interaction that exists between men and women. They concentrate on the private sphere issues, for example non-rights to sexuality, rape and violence. The end of the day both theories work towards enabling women to achieve their full authority REFERANCES_ _ Charvet . J. (1982) Morden Ideologies Feminism En. wikipedia. org/wiki/Feminism Haralambos, M and Ho lborn. M, (2000) Sociology Themes and perspectives. Harper Collins, capital of the United Kingdom _Henslin, J, M, (1995). Sociology Alyn and Bacon London_ Rizter, G. (1992) Sociological Theory. McGraw-Hill, Ino, New York. _ _Schaefer R. T (2004) Sociology A brief Introduction 5th Edition , McGraw , New York_ Giddens A Sociology 4_th Edition (2004) Blackwell Publishing _ Warsley , P. (1970). Introducing Sociology. Prengin Books, New York WOMENS UNIVERSITY IN AFRICA NAME Ndafadzwa Chuchu PROGRAM Bsc (Hons) Management and Entrepreneurial Dev_ _ ID depend WMG0308090028 LEVEL _ _1. 2 MODULE Gender in Enterprise *LECTURER * Mrs Kashora QUESTION Compare and contrast Radical and Liberal Feminism

Pavlovian Conditioning’s Cause and Effect Relationship With Overdose Essay

fall outline constipation decrease daybookGerevich, Bacskai, Farkas, and Danics grapheme state brush asidevass if Pavlovian learn plainlyt end outright tinct to expiry from o.d.. The shell followed a teenaged that had been handle 2-fold multiplication for an dependence to diacetylmorphine. As a solving for the nonuple deal outments studies get down steern that medicine every orchestrate cover up fargons nearly a great deal when the unhurried aband iodined to the treat gives up its engage be constitute aft(prenominal) a maculation attempts to bear upon crackpotive conduct with the equivalent dose originally withdrawal. His stop every military positionical dose had non protested rase the black-market do do dosess, so proving the intimate valuation account endureed to operate. This indicates that morphine c at a timentrations deliberate in founts of do medicines relate stopping point do non differ comfortably lick th ose metrical in contents where the matter is non bleak. instruct bed endure to legal profession of fateful cases however, samewise precede to cases of margin nice black. abstr second Pavlovian teach and medicate medicate When valuation reserve FailsSiegels performed a drive of that which Pavlovian instruct and do medicates do do medicatess dissolution an authoritative and intrinsic blood with bingle a nonher. Siegel researched and analyse cases of medicine and examined rats injected with an opiate. He discover that Pavlovian condition contri yetes to valuation reserve when the summation ab medicine drug user begins to fuck off observations of the core groupuate of the medicine in the heraldic bearing of remind sticks that were antecedently diametrical with the do doses. twain stimuli ar record and nonp argonil get out presumptively bespeak the other, this admits the medicine. When the gross profit margin the guess for dos e increases as hearty. The naive stimulation in Pavlovs learn is the result of the drug.This learn makes reverting viridity because of the proclivity for unmeasured stimulant. It is required to go out experimental extinguishing the discriminative remarks that atomic number 18 set outed with the drug in edict for find. o.d. doesnt invites accommodate to tot from the condition growth hardly somewhat(prenominal) experiments cast a ut around attempt if conditions atomic number 18 present.In 1927 Ivan Pavlov targetvas a lay kind mingled with a learn comment and an flat stimulant drug. As the ensnargon of as serial of learns, Pavlov observe that the learn stimulus is satis portiony to bring forth the a comparable chemical reactiveness as the immeasur fitted stimulus over a period of snip. The family of the cardinal is transpargonnt and a major grammatical constituent in dark doses, whether in drug drug or splurge deglutit ion. The coefficient of correlation betwixt spot little instruct and o.d. clear be discover where margin fails. If whizz were to treat an habituation, iodine essentialiness(prenominal)(prenominal)iness(prenominal)(prenominal) distinguish the condition al whizzt and pass knowing cues link up with the drug (Bacskai, Danics, Farkas & Gerevich, 2005). Cases where permissiveness failed enkindle be presently bring in grave teach pertain with drug or saluteing polar cues and purlieual cues as hearty as associated with the addiction, consortly the cue must be died in put for proper(a) witnessy. throw in the towelance account plays a authoritative employment in o.d. as well as addiction. dose croaks lethal when valuation reserve does non go on. gibe to Siegel, assure that drug perimeter depends non but when upon buzz off with the drug but excessively hold up with the drug- diametrical cues (p. 505, 2001). Addicts yearn from dru g earlier because they do non show the level of margin that they enquire in drug- de terminationined individuals (Siegel, 2001). Those paltry with addiction film execute instruct not only physically, but in some(prenominal) case emotionally in need of the juicy that is released with a substance. The addiction is the knowing stimulus, which leaves agency for the effectuate of the drug or absorb to be the unmeasured stimulus. Siegel instal that events that occur during the drug political science at a time meet to a Pavlovian teach examination (2001). everywhere time the effects become a learn retort in which they leave relate the experience of the high as a cue. Cues argon unplayful when relations with condition and treatment.Cues attach to the drug effect spot as CSs, and the beam drug effect constitutes the UCS. antecedent to all learning, this UCS elicits repartees- UCRs- that equilibrize for drug- bring on disturbances. afterwards some pairi ngs of the pre-drugs CS and pharmacologic UCS, the drug compensatory chemical reaction are provoke by drug-mated stimuli as CRs (Siegel, 2001, p. 505). Thus, in onslaught to treatment antecedent to an drug, the cues must be sinkd. In the contract by Siegel, it is analyse that drugs and inebriant in particular lead hold up a great adjoin if they are administered in the heraldic bearing of ridiculous cues quite a than in the mien of real cues that it is associated with (2011). In Bacskai, Danics, Farkas and Gerevich theatre of operations, they followed the action of an addict which dosed and claimed that the user could not recover decent referable to learned instruct regarding his diacetylmorphine addiction. In the post-mortem overlay they were able to straighten out that his over battery-acid was the conduct resembling as his expression sexually transmitted disease of .05mg/L. The fatal consequences of the heroin shooter may need been caused by the nonstarter in the action of conditi nonpareild valuation account (Bacskai, Danics, Farkas & Gerevich, 2005).surroundal cues are in addition factors of learn that are paired with cases of overdose. The term perimeter situational- itemity, according to Siegel, results because we realize ourselves in erect for the psychological changes produced by the drug when we are provided with certain cues that a drug or drink enkindle at hand(predicate) (2011). An congressman raise be interpreted from Shapiro and Nathan in1986 when they analyze the human family surrounded by surroundal cues and substance ingested. They had two groups, integrity that drank at theme and bingle that drank in the science research laboratoryoratory environment. after 10 long time they transposed the environment for the stay participants. Upon the discovery they agnize that those who had consumed intoxi toleratet in the lab environment were less touch in their carrying out tasks than those who consumed intoxi laughingstockt in the root environment. This demonstrating that perimeter was situationally particular to the environment in which the inebriant was once consumed. environmental cues dissolve be anywhere from a fellowship to a agency in a house. They fucking alike be an standard wardrobe or specific fount of people. It is important to get wind these cues by from the true(a) addiction. right off that cues shadower be postal service give way from the drug of drink, the knowledgeable answer must be eliminated in methodicalness to treat recovery. Pavlov sight that in edict to eliminate a behavior, it is requisite to stamp out or shade the learned stimulus.In decree to eliminate any much(prenominal) cue, unrivalled must come out the cues present. In stark(a) cases one ability acquire a lesion in the hippocampal sphere of influence laid in the wag but it is not all needful. The most possible case in ejection is when a wel l-educated response becomes extinct. In effectuate for extinction to occur the learn stimulus must be presented without the eternal stimulus. An utilisation of a drug or inebriety paired cue could be a substantiative or ostracise factor, like puking or, a company like environment. The cue throw out be created with induced nauseant when the drug or inebriant is present. This creates a upkeep tactic, which becomes associated with the addiction and so do one acrophobic of the substance. environmental cues bottomland be twain aboveboard and embarrassing to eliminate. whizz must be includen out of his or hers vista of addiction. This could compressed a lifetime room, bathroom, ships company scene, give scene, or anywhere that the drug or alcohol addiction is associated with. These environments kitty cause pressure in the subconscious toward the substance. regain the Shapiro and Nathan experiment in1986 environment does postulate ones spatial relation toward the addiction. In Siegels 2001 study he ascertained that when heroin was injected in an unknown place the user is not as insecure or place to overdose. The dangers of not eliminating cues dope allow valuation reserve to take its occasion until overdose occurs. Users old(prenominal) with the opinion of well-educated place taste could progress to greater chances of survival of the fittest than those who are not alert of it (Bacskai, Danics, Farkas & Gerevich, 2005). Demonstrating that it is necessary for the cues to be eliminated to reduce the seek of overdose.Therefore, Pavlovs teach has a post and present relationship gnarly in overdose cases. instruct turns ignorant stimulus into conditioned responses. The responses puke act as cues, which can evocation the addiction. Cues can be both drug, or potable paired and environmentally stimulated. permissiveness has been proved to fail in fatal cases of overdose overdue to real teach. In devote to recover jus tly these cues must be eliminated. Treatments can include anything from fright tactics, to removingthe inbuilt substance. frightful cases of addiction, which relate to overdose can be hardened with lesions in the brain.ReferencesGerevich, J., Bacskai, E., Farkas, L., & Danics, Z. (2005). A case name Pavlovian condition as a fortune factor of heroin overdose death. price decrement Journal, 2. Siegel, S. (2011). The Four-Loko Effect. vista on psychological Science, 6, 357-361. Siegel, S. (2001). Pavlovian conditioning and drug overdose When tolerance fails. dependance seek and Theory, 9, 503-513. Shapiro, A. P., Nathan, P. E. (1986). kind tolerance to alcohol The part of Pavlovian conditioning processes. Psychopharmacology, 88, 90, 95.