Evaluating the Impedance Field through several transport models: a comparison

J. APPL. PHYS

Voltage controlled terahertz transmission through GaN quantum wells

We report measurements of radiation transmission in the 0.220--0.325 THz frequency domain through GaN quantum wells grown on sapphire substrates at room and low temperatures. A significant enhancement of the transmitted beam intensity with the applied voltage on the devices under test is found. For a deeper understanding of the physical phenomena involved, these results are compared with a phenomenological theory of light transmission under electric bias relating the transmission enhancement to changes in the differential mobility of the two-dimensional electron gas

Shot-noise anomalies in nondegenerate elastic diffusive conductors

We present a theoretical investigation of shot-noise properties in nondegenerate elastic diffusive conductors. Both Monte Carlo simulations and analytical approaches are used. Two new phenomena are found: (i) the display of enhanced shot noise for given energy dependences of the scattering time, and (ii) the recovery of full shot noise for asymptotic high applied bias. The first phenomenon is associated with the onset of negative differential conductivity in energy space that drives the system towards a dynamical electrical instability in excellent agreement with analytical predictions. The enhancement is found to be strongly amplified when the dimensionality in momentum space is lowered from 3 to 2 dimensions. The second phenomenon is due to the suppression of the effects of long range Coulomb correlations that takes place when the transit time becomes the shortest time scale in the system, and is common to both elastic and inelastic nondegenerate diffusive conductors. These phenomena shed new light in the understanding of the anomalous behavior of shot noise in mesoscopic conductors, which is a signature of correlations among different current pulses.Comment: 9 pages, 6 figures. Final version to appear in Phys. Rev.

The nightlife spaces: the case of bush bars in Abuja

Night time has been constantly neglected in the field of urban studies. Most of the literature in the fields of Urban Geography and Sociology has examined the daytime temporal space, neglecting the nocturnal dynamics. In fact, for only about a decade, geographical works in the sphere of night studies have taken place. This contribution, starting from the reflections of Lefebvre (1991) who claimed that specific activities took place and still take place only at night, examines particular meeting places such as bush bars, which are typical nightclubs developed in Nigeria in recent times. Present in the capital Abuja and not only, closed during the day, they come to life at dusk and are placed in the green areas of urban and peri-urban spaces; finally they enliven the African night and, under the glow of the moon and the stars, they are also the meeting place where meetings take place and important decisions are taken, they are not only a place for fun and entertainment. The aim of the qualitative research, targeted at a sample of convenience, is to inform, to make known how in an urban space referred to a capital of an African country such as Nigeria there can be particular places of aggregation not present in the western cities that they try to imitate, both from design and skyline and in the construction of relational and social dynamics, related to night entertainment

Migrants inside and outside Africa. Motivations, Paths and Routes

The phenomenon of migration has always existed during the history of man since the beginning of time, just think of the history of the diaspora of the Jewish people until the great migrations of the nineteenth century which involved several European peoples, including Italians, Germans, Poles, and non-Europeans, such as the Japanese, heading to North or South America. This article, using official sources provided by IOM, UNHCR and other accredited international statistical sources, aims to offer a critical reflection about the motivations, routes and paths of migrants outside and inside Africa, showing that only a small part of them reach Europe. In fact, the first attractive centre for internal migration is C\uf4te d'Ivoire, one of the countries, together with Nigeria, which is the driving force behind the sparsely populated economy of West Africa, rich in agricultural raw materials (starting with cocoa and coffee). Finally, particular attention is given to the Italian case because is the geographical area most affected by the landings of migrants. In fact, hostility towards migrants in Italy at the end of last year was on the increase: one Italian in two said he considered immigrants a danger and was afraid of it

New insights into electron spin dynamics in the presence of correlated noise

The changes of the spin depolarization length in zinc-blende semiconductors when an external component of correlated noise is added to a static driving electric field are analyzed for different values of field strength, noise amplitude and correlation time. Electron dynamics is simulated by a Monte Carlo procedure which keeps into account all the possible scattering phenomena of the hot electrons in the medium and includes the evolution of spin polarization. Spin depolarization is studied by examinating the decay of the initial spin polarization of the conduction electrons through the D'yakonov-Perel process, the only relevant relaxation mechanism in III-V crystals. Our results show that, for electric field amplitude lower than the Gunn field, the dephasing length shortens with the increasing of the noise intensity. Moreover, a nonmonotonic behavior of spin depolarization length with the noise correlation time is found, characterized by a maximum variation for values of noise correlation time comparable with the dephasing time. Instead, in high field conditions, we find that, critically depending on the noise correlation time, external fluctuations can positively affect the relaxation length. The influence of the inclusion of the electron-electron scattering mechanism is also shown and discussed.Comment: Published on "Journal of Physics: Condensed Matter" as "Fast Track Communications", 11 pages, 9 figure

Low oxygen tension primes aortic endothelial cells to the reparative effect of tissue-protective cytokines

Erythropoietin (EPO) has both erythropoietic and tissue-protective properties. The EPO analogues carbamylated EPO (CEPO) and pyroglutamate helix B surface peptide (pHBSP) lack the erythropoietic activity of EPO but retain the tissue-protective properties that are mediated by a heterocomplex of EPO receptor (EPOR) and the β common receptor (βCR). We studied the action of EPO and its analogues in a model of wound healing where a bovine aortic endothelial cells (BAECs) monolayer was scratched and the scratch closure was assessed over 24 h under different oxygen concentrations. We related the effects of EPO and its analogues on repair to their effect on BAECs proliferation and migration (evaluated using a micro-Boyden chamber). EPO, CEPO and pHBSP enhanced scratch closure only at lower oxygen (5%), while their effect at atmospheric oxygen (21%) was not significant. The mRNA expression of EPOR was doubled in 5% compared to 21% oxygen, and this was associated with increased EPOR assessed by immunofluorescence and Western blot. By contrast βCR mRNA levels were similar in 5% and 21% oxygen. EPO and its analogues increased both BAECs proliferation and migration, suggesting that both may be involved in the reparative process. The priming effect of low oxygen tension on the action of tissue-protective cytokines may be of relevance to vascular disease, including atherogenesis and restenosis

Arachidonic Acid Metabolism In Murine Fibrosarcoma Cells With Differing In Vivo And In Vitro Characteristics

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144314/1/ijc1985363383.pd

Keratinocyte stimulation of matrix metalloproteinase-1 production and proliferation in fibroblasts: regulation through mitogen-activated protein kinase signalling events

Incubation of human dermal fibroblasts in keratinocyte-conditioned culture medium led to a 5.7-fold increase in the level of matrix metalloproteinase-1. Virtually all of the matrix metalloproteinase-1 – inducing activity could be related to agonists acting through members of the epidermal growth factor receptor family or to agonists acting through the interleukin-1 receptor. The same keratinocyte-conditioned medium also induced a modest increase in fibroblast proliferation (approximately 1.8-fold). Growth-stimulating activity could be attributed to epidermal growth factor receptor (but not interleukin-1 receptor) function. In fibroblasts exposed to keratinocyte-conditioned medium, mitogen-activated protein kinase signalling through both the extracellular signal-related kinase pathway and p38 pathway occurred. When recombinant epidermal growth factor or recombinant interleukin-1β were used as a control, they induced mitogen-activated protein kinase signalling consistent with the combined effects of epidermal growth factor receptor – specific and interleukin-1 receptor – specific agonists in keratinocyte-conditioned medium. Recombinant epidermal growth factor stimulated both matrix metalloproteinase-1 induction and proliferation while recombinant interleukin-1β stimulated matrix metalloproteinase-1 elaboration but not fibroblast growth. An inhibitor of extracellular signal-related kinase pathway signalling (U0126) blocked induction of matrix metalloproteinase-1 production induced by keratinocyte-conditioned medium (as well as by epidermal growth factor or interleukin-1β), and also inhibited proliferation. A p38 signalling inhibitor (SB203580) blocked matrix metalloproteinase-1 elaboration induced by keratinocyte-conditioned medium or interleukin-1β, but did not inhibit matrix metalloproteinase-1 elaboration or cell growth induced by epidermal growth factor. These data indicate that keratinocyte-fibroblast interactions are mediated by multiple stimulating agents acting on specific receptors to induce signalling through different mitogen-activated protein kinase pathways leading to altered expression of key biological functions