1,476 research outputs found
Spectral weight transfer in a disorder-broadened Landau level
In the absence of disorder, the degeneracy of a Landau level (LL) is
, where is the magnetic field, is the area of the sample
and is the magnetic flux quantum. With disorder, localized states
appear at the top and bottom of the broadened LL, while states in the center of
the LL (the critical region) remain delocalized. This well-known phenomenology
is sufficient to explain most aspects of the Integer Quantum Hall Effect (IQHE)
[1]. One unnoticed issue is where the new states appear as the magnetic field
is increased. Here we demonstrate that they appear predominantly inside the
critical region. This leads to a certain ``spectral ordering'' of the localized
states that explains the stripes observed in measurements of the local inverse
compressibility [2-3], of two-terminal conductance [4], and of Hall and
longitudinal resistances [5] without invoking interactions as done in previous
work [6-8].Comment: 5 pages 3 figure
Detecting the direction of a signal on high-dimensional spheres: Non-null and Le Cam optimality results
We consider one of the most important problems in directional statistics,
namely the problem of testing the null hypothesis that the spike direction
of a Fisher-von Mises-Langevin distribution on the -dimensional
unit hypersphere is equal to a given direction . After a reduction
through invariance arguments, we derive local asymptotic normality (LAN)
results in a general high-dimensional framework where the dimension goes
to infinity at an arbitrary rate with the sample size , and where the
concentration behaves in a completely free way with , which
offers a spectrum of problems ranging from arbitrarily easy to arbitrarily
challenging ones. We identify various asymptotic regimes, depending on the
convergence/divergence properties of , that yield different
contiguity rates and different limiting experiments. In each regime, we derive
Le Cam optimal tests under specified and we compute, from the Le Cam
third lemma, asymptotic powers of the classical Watson test under contiguous
alternatives. We further establish LAN results with respect to both spike
direction and concentration, which allows us to discuss optimality also under
unspecified . To investigate the non-null behavior of the Watson test
outside the parametric framework above, we derive its local asymptotic powers
through martingale CLTs in the broader, semiparametric, model of rotationally
symmetric distributions. A Monte Carlo study shows that the finite-sample
behaviors of the various tests remarkably agree with our asymptotic results.Comment: 47 pages, 4 figure
Non-Equilibrium Edge Channel Spectroscopy in the Integer Quantum Hall Regime
Heat transport has large potentialities to unveil new physics in mesoscopic
systems. A striking illustration is the integer quantum Hall regime, where the
robustness of Hall currents limits information accessible from charge
transport. Consequently, the gapless edge excitations are incompletely
understood. The effective edge states theory describes them as prototypal
one-dimensional chiral fermions - a simple picture that explains a large body
of observations and calls for quantum information experiments with quantum
point contacts in the role of beam splitters. However, it is in ostensible
disagreement with the prevailing theoretical framework that predicts, in most
situations, additional gapless edge modes. Here, we present a setup which gives
access to the energy distribution, and consequently to the energy current, in
an edge channel brought out-of-equilibrium. This provides a stringent test of
whether the additional states capture part of the injected energy. Our results
show it is not the case and thereby demonstrate regarding energy transport, the
quantum optics analogy of quantum point contacts and beam splitters. Beyond the
quantum Hall regime, this novel spectroscopy technique opens a new window for
heat transport and out-of-equilibrium experiments.Comment: 13 pages including supplementary information, Nature Physics in prin
Dynamic response of a cracked atomic force microscope cantilever used for nanomachining
The vibration behavior of an atomic force microscope [AFM] cantilever with a crack during the nanomachining process is studied. The cantilever is divided into two segments by the crack, and a rotational spring is used to simulate the crack. The two individual governing equations of transverse vibration for the cracked cantilever can be expressed. However, the corresponding boundary conditions are coupled because of the crack interaction. Analytical expressions for the vibration displacement and natural frequency of the cracked cantilever are obtained. In addition, the effects of crack flexibility, crack location, and tip length on the vibration displacement of the cantilever are analyzed. Results show that the crack occurs in the AFM cantilever that can significantly affect its vibration response
Dehydroepiandrosterone inhibits the progression phase of mammary carcinogenesis by inducing cellular senescence via a p16-dependent but p53-independent mechanism
INTRODUCTION: Dehydroepiandrosterone (DHEA), an adrenal 17-ketosteroid, is a precursor of testosterone and 17β-estradiol. Studies have shown that DHEA inhibits carcinogenesis in mammary gland and prostate as well as other organs, a process that is not hormone dependent. Little is known about the molecular mechanisms of DHEA-mediated inhibition of the neoplastic process. Here we examine whether DHEA and its analog DHEA 8354 can suppress the progression of hyperplastic and premalignant (carcinoma in situ) lesions in mammary gland toward malignant tumors and the cellular mechanisms involved. METHODS: Rats were treated with N-nitroso-N-methylurea and allowed to develop mammary hyperplastic and premalignant lesions with a maximum frequency 6 weeks after carcinogen administration. The animals were then given DHEA or DHEA 8354 in the diet at 125 or 1,000 mg/kg diet for 6 weeks. The effect of these agents on induction of apoptosis, senescence, cell proliferation, tumor burden and various effectors of cellular signaling were determined. RESULTS: Both agents induced a dose-dependent decrease in tumor multiplicity and in tumor burden. In addition they induced a senescent phenotype in tumor cells, inhibited cell proliferation and increased the number of apoptotic cells. The DHEA-induced cellular effects were associated with increased expression of p16 and p21, but not p53 expression, implicating a p53-independent mechanism in their action. CONCLUSION: We provide evidence that DHEA and DHEA 8354 can suppress mammary carcinogenesis by altering various cellular functions, inducing cellular senescence, in tumor cells with the potential involvement of p16 and p21 in mediating these effects
Thermal Properties of Graphene, Carbon Nanotubes and Nanostructured Carbon Materials
Recent years witnessed a rapid growth of interest of scientific and
engineering communities to thermal properties of materials. Carbon allotropes
and derivatives occupy a unique place in terms of their ability to conduct
heat. The room-temperature thermal conductivity of carbon materials span an
extraordinary large range - of over five orders of magnitude - from the lowest
in amorphous carbons to the highest in graphene and carbon nanotubes. I review
thermal and thermoelectric properties of carbon materials focusing on recent
results for graphene, carbon nanotubes and nanostructured carbon materials with
different degrees of disorder. A special attention is given to the unusual size
dependence of heat conduction in two-dimensional crystals and, specifically, in
graphene. I also describe prospects of applications of graphene and carbon
materials for thermal management of electronics.Comment: Review Paper; 37 manuscript pages; 4 figures and 2 boxe
Characterization of the Psychological, Physiological and EEG Profile of Acute Betel Quid Intoxication in Naïve Subjects
Betel quid use and abuse is wide spread in Asia but the physiological basis of intoxication and addiction are unknown. In subjects naïve to the habit of betel quid intoxication, the psychological and physiological profile of intoxication has never been reported. We compared the effect of chewing gum or chewing betel quid, and subsequent betel quid intoxication, on psychological assessment, prospective time interval estimation, numerical and character digit span, computerized 2 choice tests and mental tasks such as reading and mathematics with concurrent monitoring of ECG, EEG and face temperature in healthy, non-sleep deprived, male subjects naïve to the habit of chewing betel quid. Betel quid intoxication, dose dependently induced tachycardia (max 30 bpm) and elevated face temperature (0.7°C) (P<0.001) above the effects observed in response to chewing gum (max 12 bpm and 0.3°C) in 12 subjects. Gross behavioral indices of working memory such as numerical or character digit span in 8 subjects, or simple visual-motor performance such as reaction speed or accuracy in a two choice scenario in 8 subjects were not affected by betel quid intoxication. Betel quid intoxication strongly influenced the psychological aspects of perception such as slowing of the prospective perception of passage of a 1 minute time interval in 8 subjects (P<0.05) and perceived increased arousal (P<0.01) and perceived decreased ability to think (P<0.05) in 31 subjects. The EEG spectral profile recorded from mental states associated with open and closed eyes, and mental tasks such as reading and eyes closed mental arithmetic were significantly modified (P<0.05) relative to chewing gum by betel quid intoxication in 10 subjects. The prevalence of betel quid consumption across a range of social and work settings warrants greater investigation of this widespread but largely under researched drug
The Pathway to Detangle a Scrambled Gene
Programmed DNA elimination and reorganization frequently occur during cellular differentiation. Development of the somatic macronucleus in some ciliates presents an extreme case, involving excision of internal eliminated sequences (IESs) that interrupt coding DNA segments (macronuclear destined sequences, MDSs), as well as removal of transposon-like elements and extensive genome fragmentation, leading to 98% genome reduction in Stylonychia lemnae. Approximately 20-30% of the genes are estimated to be scrambled in the germline micronucleus, with coding segment order permuted and present in either orientation on micronuclear chromosomes. Massive genome rearrangements are therefore critical for development.To understand the process of DNA deletion and reorganization during macronuclear development, we examined the population of DNA molecules during assembly of different scrambled genes in two related organisms in a developmental time-course by PCR. The data suggest that removal of conventional IESs usually occurs first, accompanied by a surprising level of error at this step. The complex events of inversion and translocation seem to occur after repair and excision of all conventional IESs and via multiple pathways.This study reveals a temporal order of DNA rearrangements during the processing of a scrambled gene, with simpler events usually preceding more complex ones. The surprising observation of a hidden layer of errors, absent from the mature macronucleus but present during development, also underscores the need for repair or screening of incorrectly-assembled DNA molecules
Moderate-to-vigorous physical activity modifies the relationship between sedentary time and sarcopenia: the Tromsø Study 2015–2016
Background: Sarcopenia is an age-related muscle disease primarily characterized by reductions in muscle strength that increases the risk of falls, fractures, cognitive impairment, and mortality. Exercise is currently preferred in prevention and treatment, but it is unknown how different habitual physical activity and sedentary behaviour patterns associate with sarcopenia status. The purpose of the present study was to compare associations of these patterns with probable sarcopenia in older adults.
Methods: In 3653 community-dwelling participants (51% women) aged 60–84 years from the seventh survey of the Tromsø Study, we assessed objective physical activity and sedentary behaviour collected over 8 days (ActiGraph wGT3X-BT Accelerometer), grip strength (Jamar+ Digital Dynamometer), five-repetition chair stands, and self-reported disease. We combined tertiles of sedentary (SED) time and moderate-to-vigorous physical activity (MVPA) to create nine different activity profiles (SEDHIGH, SEDMOD, and SEDLOW combined with MVPAHIGH, MVPAMOD, or MVPALOW). Multiple logistic regression models were used to examine how these profiles associated with probable sarcopenia, defined by low handgrip strength and/or slow chair stands time according to the revised European Working Group on Sarcopenia in Older People criteria.
Results: Probable sarcopenia was present in 227 (6.2%) participants. Men with probable sarcopenia had on average 35.3 min more SED time and 20 min less MVPA compared with participants without sarcopenia (P HIGH–MVPALOW reference activity profile (714.2 min SED/day and 10.4 min MVPA/day), the SEDHIGH–MVPAMOD profile (697.1 min SED/day and 31.5 min MVPA/day) had significantly lower odds ratio (OR) for probable sarcopenia (OR 0.17, 95% confidence interval [CI] 0.08–0.35), while the SEDLOW–MVPALOW profile (482.9 min SED/day and 11.0 min MVPA/day) did not (OR 0.72, 95% CI 0.47–1.11). These findings were not influenced by age, sex, smoking, or self-reported diseases, and higher levels of MVPA did not further decrease ORs for probable sarcopenia.
Conclusions: Older adults who achieve moderate amounts of MVPA have reduced odds for probable sarcopenia, even when they have high sedentary time. Those with low sedentary time did not have reduced odds for probable sarcopenia when they also had low amounts of MVPA. These findings need confirmation in longitudinal studies but suggest that interventions for preventing sarcopenia should prioritize increasing MVPA over reducing sedentary behaviour
- …