High-Performance and Ultralow-Noise Two-Dimensional Heterostructure Field-Effect Transistors with One-Dimensional Electrical Contacts

Two-dimensional heterostructure field-effect transistors (2D-HFETs) with one-dimensional electrical contacts to atomically thin channels have recently shown great device performance, such as reduced contact resistance, leading to ballistic transport and enhanced carrier mobility. While a number of low-frequency noise studies exists on bare graphene devices supported on silicon dioxide gate insulators with surface contacts, such studies in heterostructure devices comprising epitaxial graphene on hexagonal boron nitride (hBN) with edge contacts are extremely limited. In this article, we present a systematic, temperature-dependent study of electrical transport and low-frequency noise in edge-contacted high-mobility HFET with a single atomic-layer graphene channel encapsulated by hBN and demonstrate ultralow noise with a Hooge parameter of ≈10–5. By combining measurements and modeling based on underlying microscopic scattering mechanisms caused by charge carriers and phonons, we directly correlate the high-performance, temperature-dependent transport behavior of this device with the noise characteristics. Our study provides a pathway towards engineering low-noise graphene-based high-performance 2D-FETs with one-dimensional edge contacts for applications such as digital electronics and chemical/biological sensing.acceptedVersio

Spectroscopic binaries among Hipparcos M giants II. Binary frequency

This paper is the second one in a series devoted to the study of properties of binaries involving M giants. The binary frequency of field M giants is derived and compared with the binary fraction of K giants. Diagrams of the CORAVEL spectroscopic parameter Sb (measuring the average line-width) vs. radial-velocity standard deviation for our samples are used to define appropriate binarity criteria. These then serve to extract the binarity fraction among the M giants. Comparison is made to earlier data on K giants binarity frequency. The Sb parameter is discussed in relation to global stellar parameters and the Sb vs. stellar radius relation is used to identify fast rotators. We find that the spectroscopic binary detection rate among field M giants, in a sample with a low number of velocity measurements (~2), unbiased toward earlier known binaries, is 6.3%. This is less than half of the analogous rate for field K giants, likely resulting from a real difference. This difference originates in the greater difficulty of finding binaries among M giants because of their smaller orbital velocity amplitudes and larger intrinsic jitter and in the different distributions of K and M giants in the eccentricity-period diagram. A larger detection rate was obtained in a smaller M giant sample with more radial velocity measurements per object: 11.1% confirmed plus 2.7% possible binaries. The CORAVEL spectroscopic parameter Sb was found to correlate better with the stellar radius than with either luminosity or effective temperature separately. Two outliers of the Sb vs. stellar radius relation, HD 190658 and HD 219654, have been recognized as fast rotators. The rotation is companion-induced, as both objects turn out to be spectroscopic binaries.Comment: 12 pages, 7 figures, accepted for publication in A&A, language editing changes onl

Determination of stellar parameters of C-rich hydrostatic stars from spectro-interferometric observations

Giant stars, and especially C-rich giants, contribute significantly to the chemical enrichment of galaxies. The determination of precise parameters for these stars is a necessary prerequisite for a proper implementation of this evolutionary phase in the models of galaxies. Infrared interferometry opened new horizons in the study of the stellar parameters of giant stars, and provided new important constraints for the atmospheric and evolutionary models.We aim to determine which stellar parameters can be constrained by using infrared interferometry and spectroscopy, in the case of C-stars what is the precision which can be achieved and what are the limitations. For this purpose we obtained new infrared spectra and combined them with unpublished interferometric measurements for five mildly variable carbon-rich asymptotic giant branch stars. The observations were compared with a large grid of hydrostatic model atmospheres and with new isochrones which include the predictions of the thermally pulsing phase. For the very first time we are able to reproduce spectra in the range between 0.9 and 4 $\mu$m, and $K$ broad band interferometry with hydrostatic model atmospheres. Temperature, mass, log$(g)$, C/O and a reasonable range for the distance were derived for all the objects of our study. All our targets have at least one combination of best-fitting parameters which lays in the region of the HR-diagram where C-stars are predicted. We confirm that low resolution spectroscopy is not sensitive to the mass and log$(g)$ determination. For hydrostatic objects the $3\,\mu$m feature is very sensitive to temperature variations therefore it is a very powerful tool for accurate temperature determinations. Interferometry can constrain mass, radius and log$(g)$ but a distance has to be assumed. The large uncertainty in the distance measurements available for C-rich stars remains a major problem.Comment: 18 pages, 11 figures. Accepted for publication in A&

Cool luminous stars: the hybrid nature of their infrared spectra -- Carbon, oxygen, and their isotopic abundances in 23 K - M giant stars

We identified a possible origin of the difficulty in abundance analysis of cool luminous stars. We found purely empirically that there is a limit of logW/nu = -4.75 (W: equivalent width, nu: wavenumber) above which the observed lines do not follow the line formation theory based on the classical micro-turbulent model and that the abundance analysis can be done only with the lines of logW/nu < -4.75. The C, O, and their isotopic abundances determined from such weak lines of CO and OH in 23 K - M giants are roughly consistent with the predictions of evolutionary models. However, the stronger lines of logW/nu > -4.75 cannot be analyzed at all by the classical line formation theory. From the behavior of these lines and considering other observations such as the detections of H2O lines, not only in the late M giants but also in the early M and K giants, we found that these lines are badly disturbed by the contamination from extra molecular layers. We already know that the very strong lines of logW/nu > -4.4 are contaminated by the contribution from the extra warm molecular layers, but we now show that such contamination should be prevailing not only in the strong low excitation lines but also in the intermediate-strength lines (-4.75 -4.4) as well. The reason why these lines cannot be used for determining photospheric abundances is simply because they include the contamination of the non-photospheric origin. Instead they can be new proves of the warm molecular envelope for which little is known yet. An important conclusion is that the infrared spectra of K - M giants are a hybrid of at least two components originating in the photosphere and the warm molecular envelope. In the interpretation and analysis of the infrared spectra of cool luminous stars, it is essential to keep their hybrid naure in mind.Comment: 22 pages, 18 figures, accepted for publication in A&A, corrected typo

Nonadiabatic Heating in Magnetic Reconnection

Plasma transport process as a fundamental problem in magnetospheric physics is often associated with strong nonadiabatic heating. At the magnetopause, observations show an increase of specific entropy (i.e., S = p/ργ) by 2 orders of magnitude from the magnetosheath into the magnetosphere. In the near‐Earth magnetotail, particle injection requires strongly entropy depleted plasma bubbles, and their evolution can be strongly modified in the presence of nonadiabatic heating. In this study, one of the critical plasma transport mechanisms, magnetic reconnection, is investigated as a nonadiabatic process in the framework of MHD. It is important to examine whether magnetic reconnection can provide sufficient nonadiabatic heating to explain the observed plasma properties and to identify plasma conditions that allow such strong nonadiabatic heating. We demonstrate that the entropy can indeed strongly increase associated with magnetic reconnection provided that the plasma beta (i.e., the ratio of thermal to magnetic energy density) is low in the inflow region of reconnection

Beneficial autoimmunity at body surfaces – immune surveillance and rapid type 2 immunity regulate tissue homeostasis and cancer

Epithelial cells line body surface tissues and provide a physicochemical barrier to the external environment. Frequent microbial and non-microbial challenges such as those imposed by mechanical disruption, injury or exposure to noxious environmental substances including chemicals, carcinogens, ultraviolet-irradiation or toxins cause activation of epithelial cells with release of cytokines and chemokines as well as alterations in the expression of cell surface ligands. Such display of epithelial stress is rapidly sensed by tissue resident immunocytes, which can directly interact with self-moieties on epithelial cells and initiate both local and systemic immune responses. Epithelial cells are thus key drivers of immune surveillance at body surface tissues. However, epithelial cells have a propensity to drive type 2 immunity (rather than type 1) upon non-invasive challenge or stress – a type of immunity whose regulation and function still remain enigmatic. Here we review the induction and possible role of type 2 immunity in epithelial tissues and propose that rapid immune surveillance and type 2 immunity are key regulators of tissue homeostasis and carcinogenesis

Correlates of Employment Among Welfare Recipients: Do Psychological Characteristics and Attitudes Matter?

This study examines whether and how a wide range of potential barriers to work,including psychological characteristics and attitudes, are associated with current employment in a recent sample of welfare recipients in Michigan ( N = 672 ). Psychological factors include measures of depressive symptoms, work attitudes, and perceived risks associated with leaving welfare. Over and above demographic, economic, and contextual factors, positive psychological characteristics and attitudes were found to be moderately associated with currently being employed. Implications for welfare-to-work programs and policy are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44056/1/10464_2004_Article_343149.pd

Recreational drug use and use of drugs associated with chemsex among HIV-negative and HIV-positive heterosexual men and women attending sexual health and HIV clinics in England.

BACKGROUND: There is little information on the prevalence of recreational drug use among UK heterosexual men and women, in particular on use of drugs associated with 'chemsex' within gay communities. The aim of this study was to examine among HIV-negative and HIV-positive heterosexual men and women in England: (i) the prevalence of recreational drug use (including use of drugs associated with chemsex), (ii) socio-economic/lifestyle correlates of drug use, and (iii) the association of drug use with sexual behavior measures and mental health symptoms. METHODS: Data are from the AURAH study of HIV-negative individuals attending sexual health clinics across England (2013-2014) and the ASTRA study of HIV-positive individuals attending HIV outpatient clinics in England (2011-2012). Prevalence of recreational drug use (past three months) and associations are presented separately among the four sample groups: HIV-negative (N = 470) and HIV-positive (N = 373) heterosexual men and HIV-negative (N = 676) and HIV-positive (N = 637) women. RESULTS: The age standardized prevalence of any drug use was 22.9%, 17.1%, 15.3%, and 7.1% in the four sample groups respectively. In all groups, cannabis was the drug most commonly used (range from 4.7% to 17.9%) followed by cocaine (1.6% to 8.5%). The prevalence of use of drugs associated with chemsex was very low among HIV-negative participants (1.0% heterosexual men, 0.2% women) and zero among HIV-positive men and women. In age-adjusted analysis, factors linked to drug use overall and/or to cannabis and cocaine use specifically in the four sample groups included Black/mixed Caribbean and white (vs. Black/mixed African) ethnicity, lower level of education , cigarette smoking, and higher risk alcohol consumption. Associations of recreational drug use with measures of condomless sex, depression, and anxiety were observed in the four groups, but were particularly strong/apparent among women. CONCLUSION: Providers need to be aware of cannabis and cocaine use and its potential link with sexual risk behavior and symptoms of depression and anxiety among heterosexual men and women attending sexual health and HIV clinics