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The plasma parameters of laser-ablated Zirconium (Zr) using a Langmuir probe technique have been investigated by employing a Q-switched Nd:YAG laser (532 nm, 6 ns) at various irradiances ranging from 8.6 to 15.5 GW/cm2. All the measurements have been performed under an ultra-high vacuum condition while keeping the probe at a fixed distance of 4 mm from the target. By varying the biasing voltages from 1 to 75 V, the corresponding values of electric currents are measured by the probe on the oscilloscope. Laser-induced Zr plasma parameters such as electron temperature, electron number density, plasma potential, Debye length, and thermal velocity have been evaluated from I–V characteristic curves of Langmuir probe data. It is found that both the electron temperature and thermal velocity of Zr plasma reveal an increasing trend from 18 to 41 eV and 2.8 × 108 to 4.3 × 108 cm/s, respectively, with increasing laser irradiance which is attributed to more energy deposition and enhanced ablation rate. However, the electron number density of Zr plasma exhibits a non-significant increase from 6.5 × 1014 to 6.7 × 1014 cm−3 with increasing irradiance from 8.6 to 10.9 GW/cm2. A further increase in irradiance from 12 to 15.5 GW/cm2 causes a reduction in the number density of Zr plasma from 6.1 × 1014 to 5.6 × 1014 cm−3 which is attributed to the formation of thick sheath, ambipolar electric field, and laser-supported detonation waves (Shock front). Scanning electron microscope analysis has been performed to reveal the surface morphology of irradiated Zr. It reveals the formation of cracks, ridges, cones, and grains. It was observed at high irradiances the ridges are vanished, whereas cones and cracks are dominant features. By controlling plasma parameters, surface structuring of materials can be controlled, which has a vast range of applications in the industry and medicine.
Two-photon absorption (TPA) of Au-ion irradiated glasses in the femtosecond regime has been analyzed by an open-aperture Z scan technique. Three types of glasses, namely GIL49, BK7, and Glass B were irradiated by using 1700 keV Au+ ion beams. Samples were post-annealed at 600°C for 5 h. Penetration depth and distribution of Au+ ions having 1700 keV energy within glass substrates were estimated by transport of ions in matter (TRIM) simulations. Detailed calculations with full-damage cascades were performed for each sample, taking into account the chemical composition of glass substrates. TRIM results reveal that there is no significant change in ion range, straggling, and ion distribution with the change in the substrate composition. However, Z scan results showed a difference in TPA coefficients for all three glasses. Extent of crosslinking within each of irradiated sample, owing to its chemical composition, may have affected their TPA coefficients.
The effect of laser fluence and nature of ambient environments on the sputtering yield, surface modifications, crater depth, UV-visible absorption spectra, chemical composition, and micro hardness of Zr has been investigated. Nd: YAG laser (532 nm, 10 Hz, 6 ns) at different fluences varying from 16 to 60.8 Jcm−2 was employed as an irradiation source. All measurements are performed under two ambient environments of Ar and O2 at a constant pressure of 10 Torr. Quartz crystal microbalance has been employed for the measurement of sputtering yield of laser irradiated Zr. It is revealed that sputtering yield increases monotonically with increasing fluence under both environments however, it is higher in Ar as compared to O2 environment. Scanning electron microscope (SEM) has been used to explore the surface morphology. SEM analysis exhibits the formation of cones, ridges, and cracks at the central ablated areas whereas, laser-induced periodic surface structures, periodic ridges and sharp cones are observed at inner boundaries in both environments of Ar and O2. Sharp spikes are observed in both environments, however, their height and distinctness are more pronounced in Ar as compared to O2. Cones are characteristic features in Ar, whereas, cavities and channels are dominant features in O2 environment at outer boundaries. The formation and growth of surface structures are dependent upon laser fluence and ambient gas nature. The depth profilometry has been used to measure the crater depth of irradiated Zr target by using an optical microscope. UV visible spectroscopy and energy-dispersive X-ray analyses reveal the oxide formation in the case of Zr irradiation in O2 environment. The Vicker Micro-hardness tester has been employed to measure the hardness. The higher observed values of sputtering yield, crater depth and hardness of laser ablated Zr in Ar as compared to O2 are well correlated with distinct surface structures.
Aerogels are light-weight porous materials that can tolerate the processing steps required for designing and creating an electric circuit such that the aerogel can be utilized as a substrate for device fabrication. Previous studies have shown the biostability and biocompatibility of polyurea crosslinked silica aerogels both in vivo and in vitro and have demonstrated the potential use of aerogels in biomedical applications. In vitro studies have shown that in the presence of an applied electric field neurites regeneration rate was greater on crosslinked silica aerogels than on tissue culture petridish used as a positive control. Currently, epineural suturing and nerve grafting are the gold standards for surgical reconstruction of injured nerves. However, because they rely on passive mechanisms for reapproximating the distal and proximal terminals they often lead to partial or no recovery leaving room for improvement. The present study investigates the feasibility of a wireless aerogel–based electrically-stimulating implant intended for nerve repair applications. Here the authors report on RF coupling between a secondary coil and a primary coil to wirelessly energize an interdigitated electrode array consisting of eleven interlocking fingers, created on a silica aerogel substrate. The coupling strength was tested both in air and in an animal model, as a function of distance and will be reported. This study focuses on in vivo evaluation and feasibility assessment of a novel active 3-D aerogel-based peripheral nerve repair device. The device utilizes induced EMF to establish a current (hence electrical stimulation) in predetermined pathways where nerve stumps will be confined to. Fundamental differences between in vitro and in vivo models necessitate the in vivo approach. The novel inductively-powered electrical stimulation aerogel-based device utilizes previously established 3-D confinement method for immobilization of nerve stumps, taking advantage of the mesoscopic surface roughness, unique to aerogels. The technique is tested on a mechanically strong, lightweight, porous, and biostable aerogel. Lithographic techniques, gold (Au) thin film metallization, and Faraday induction is used for circuit design, development, and activation.
By the time of his death in 2003, Edward Said was one of the most famous literary critics of the twentieth century. Said's work has been hugely influential far beyond academia. As a prominent advocate for the Palestinian cause and noted cultural critic, Said redefined the role of the public intellectual. This volume explores the problems and opportunities afforded by Said's work: its productive and generative capacities as well as its in-built limitations. After Said captures the essence of Said's intellectual and political contribution and his extensive impact on postcolonial studies. It examines his legacy by critically elaborating his core concepts and arguments. Among the issues it tackles are humanism, Orientalism, culture and imperialism, exile and the contrapuntal, realism and postcolonial modernism, world literature, Islamophobia, and capitalism and the political economy of empire. It is an excellent resource for students, graduates and instructors studying postcolonial literary theory and the works of Said.
In the scholarly argument over whether slavery was primarily a social, economic, or political phenomenon, Mier and Kopytoff take a benign view. They argue that slavery mainly served to assimilate slaves into the slave masters’ households as kinsmen. Hopkins disagrees. Building on Nieboer and Domar, he points to the use of coercion, and stresses that in the context of land abundance, labor scarcity, and simple agricultural technology, “the costs of acquiring and maintaining slaves were less than the costs of hiring labour.” Hopkins's approach is therefore centered on economic choice, and it assumes that slavery was primarily an economic institution: that the essence of the slave's role mainly resided in his labor, and that slaves were chattel. Meillassoux's contribution to the debate over the nature of slavery in Africa recognizes that slavery could be, but was not always necessarily, primarily a political institution, and that the basis of slavery was violence. It also stresses confl icts between masters and slaves, as well as an emphasis on the organization of production. For Klein and other scholars, both Hopkins's and Meillassoux's approaches are most appropriate for high-density slave systems such as the Sokoto caliphate. The evidence confirms that Klein and others are right. In particular, it shows that most slaves were enslaved by violence, that they were considered property, that they were not always treated mildly, and that they often resisted against their subordination. It also reveals the economic dimensions of slavery, by stressing that slaves were used for agricultural production and other economic tasks, that they were viewed as property, and that slaves who worked on their own account typically paid their masters significant amounts, which contributed to their inability to purchase their own freedom.
Although Hopkins's and Meillassoux's arguments can be extended to the Sokoto caliphate, one question remains unanswered or has not been adequately addressed by scholars: why in the Sokoto caliphate and other such high-density slave systems, unlike in many other parts of Africa, we do not find the assimilation of most plantation slaves into the masters’ households as kinsmen, or (in other words) how was the development of serfdom prevented?
Genuine “slave economies”—in which slave labour permeated all sectors of the economy and played a central role in economic output outside the sphere of family labour—were rare in history.’ Classical Greece and the Italian heartland of the Roman empire are among the most notable cases. This raises important questions: how did the Greeks and Romans come to join this exclusive club, and how did the circumstances that determined the development and structure of their regimes of slave labour compare to those that shaped other slave-rich systems?
With these words, Walter Scheidel began his interesting recent article on the expansion and nature of slavery in Classical Greece and Republican Rome. Read at its broadest, though dealing with very similar issues largely related to the development and nature of slavery in highdensity slave systems, as well as with the theme of comparative slavery, the present work, rather than focusing primarily on slavery in Classical Greece and Republican Rome, primarily focuses on plantation slavery in the largest Islamic state of nineteenth-century West Africa: the Sokoto caliphate.
The Sokoto caliphate (1804–1903) was situated in the central Sudan region of West Africa. It comprised two ecological zones: the Sudan savanna and the Guinea savanna. The former covered the northern parts of the caliphate, while the latter prevailed in the southern parts of the state. The soil types in the Guinea savanna support the production of diverse crops such as yam, cassava, guinea corn, cotton, tobacco, soy beans, cowpeas, and rice, while those in the Sudan savanna are more favorable for the production of cereals (millet, sorghum, maize, and rice), cotton, groundnuts, and legumes, as well as for livestock rearing.
The caliphate was established through a jihad led by a Fulani cleric known as Usman dan Fodio at the beginning of the nineteenth century. Hausaland was the principal theater of the jihad. Before the jihad, Hausaland consisted of several centralized Hausa governments or city states that were organized around markets, palaces, towns, and “closely settled zones.” These Hausa states had a long history of involvement in international trade, and by 1500 most of their rulers had embraced Islam. On the eve of the jihad, the Hausa states were ruled by nominal Muslims, and they were at war with each other.
The Sokoto caliphate covered a vast expanse of land that consisted of former Hausa states such as Gobir and Zamfara. Plantations could be found in most if not all of these states, as well as in other parts of the central Sudan, in both the Sudan savanna and Guinea savanna belts, even before the nineteenth-century Sokoto jihad. But the jihad and its aftermath encouraged the rapid expansion of the existing plantation sector, at least in the region that became known as the Sokoto caliphate; without the holy war, plantation expansion probably would not have been as notable.
From the earliest studies of the problem of slavery scholars have tried to explain how slavery, as an institution, developed. Nieboer's explanation linked land abundance to slavery, and he stressed that the use of slaves in societies having abundant land was a means of enhancing agricultural production or economic output in general. Following Nieboer, some scholars have identified demographic conditions of low population-to-land ratios in Africa, and noted that the availability of land that people could fl ee to in order to avoid working for others resulted in efforts to check labor mobility, and ultimately to the reliance on plantation slavery and other forms of coerced labor. Put differently, they, like Nieboer, noted that slavery was exclusively a response to economic incentives associated with land availability. Other scholars argue that land-labor pressures alone cannot explain how slavery and other forms of unfree labor developed. In so doing they stress that the development or cause of slavery in Africa was mainly tied to social or political factors.
Although we do not have data like Austin and other scholars had, to determine whether or not slave labor was cheaper than other forms of labor, clearly land abundance characterized pre-jihad Hausaland, and clearly plantation slavery was in the economic best interest of slaveholders, as chapter 6 of this book will demonstrate. Given these two facts, the present chapter accepts that plantation slavery in the Sokoto caliphate was partly a response to economic incentives associated with land availability. However, it argues that the origin of plantation slavery there was more closely associated with political policy, particularly with Bello's interest in economic and political consolidation, as well as with his interest “with the maintenance of an active front line for defense and annual campaigns.”
The Sokoto jihad was spearheaded by men of vision who were mainly concerned with the establishment of a just, ideal, and viable Islamic state modeled after that centered in Arabia in the seventh century. The consensus among these men was that Muslims are destined to rule over unbelievers, and that trade in enslaved Muslims was wrong. Among other factors, this resulted in the use of military action to support their vision. The nature and course of the resulting military engagements led to increased availability of land and slaves, which in turn fostered plantation development.
State Policy Goals, Innovations, and Plantation Development
Although the policy goals pursued by the Sokoto jihad leaders were in many respects consistent with those of the various Hausa regimes they displaced, they differed significantly, in part because they were primarily shaped by Islamic principles, and in part because the basis for these policies was the Muslim ummah, or broader Islamic community, rather than the limited regional interests which had underpinned the policies of the old regimes. It is not necessary to examine the pre-jihad and the post-jihad policy goals in detail. However, it is crucial to state that, unlike the pre-jihad leaders, their successors extensively documented their concerns. They wrote on diverse issues such as education, personal integrity, finance, and administration. The jihad leaders, however, were primarily concerned with the establishment of a just, viable, and ideal Islamic state modeled after the historic state centered in Arabia in the seventh century. In conformity with the ideals that inspired the jihad, they presented their policy objectives in religious terms. For instance, Usman dan Fodio's writings suggest that his concern with the establishment of a state and with the security of Muslim interests in general was connected with his belief that Muslims were obliged to reject domination by unbelievers, either by overthrowing them or by fl ight. In articulating this position and relating it to his local context, he, in explicitly Islamic ideological terms, considered his followers as jama'a and the pre-jihad Hausa rulers as unbelievers, because they had mixed Islam with “indigenous” religious practices:
Another class [of “unbelievers’ lands”] is those lands where Islam predominates and unbelief is rare such as Borno, Kano, Katsina, Songhay, and Mali according to the examples given by Ahmad Baba in the aforementioned book [Al-Kashf wa'l-bayan].