775 research outputs found
Negative longitudinal magnetoresistance in GaAs quantum wells
Negative longitudinal magnetoresistances (NLMRs) have been recently observed
in a variety of topological materials and often considered to be associated
with Weyl fermions that have a defined chirality. Here we report NLMRs in
non-Weyl GaAs quantum wells. In the absence of a magnetic field the quantum
wells show a transition from semiconducting-like to metallic behaviour with
decreasing temperature. We observed pronounced NLMRs up to 9 Tesla at
temperatures above the transition and weak NLMRs in low magnetic fields at
temperatures close to the transition and below 5 K. The observed NLMRs show
various types of magnetic field behaviour resembling those reported in
topological materials. We attribute them to microscopic disorder and use a
phenomenological three-resistor model to account for their various features.
Our results showcase a new contribution of microscopic disorder in the
occurrence of novel phenomena. They may stimulate further work on tuning
electronic properties via disorder/defect nano-engineering
Environmental Effect on the Associations of Background Quasars with Foreground Objects: II. Numerical Simulations
Using numerical simulations of cluster formation in the standard CDM model
(SCDM) and in a low-density, flat CDM model with a cosmological constant
(LCDM), we investigate the gravitational lensing explanation for the reported
associations between background quasars and foreground clusters. Under the
thin-lens approximation and the unaffected background hypothesis , we show that
the recently detected quasar overdensity around clusters of galaxies on scales
of arcminutes cannot be interpreted as a result of the gravitational
lensing by cluster matter and/or by their environmental and projected matter
along the line of sight, which is consistent with the analytical result based
on the observed cluster and galaxy correlations (Wu, et al. 1996). It appears
very unlikely that uncertainties in the modeling of the gravitational lensing
can account for the disagreement between the theoretical predictions and the
observations. We conclude that either the detected signal of the quasar-cluster
associations is a statistical fluke or the associations are are generated by
mechanisms other than the magnification bias.Comment: 15 pages, 5 figures, accepted for publication in Ap
Cytotoxicity of Essential Oil of Chenopodium ambrosioides L against Human Breast Cancer MCF-7 Cells
Purpose: To investigate the cytotoxic activity of the essential oil of Chenopodium ambrosioides L. against human breast cancer MCF-7 cells.Methods: Cytotoxicity was characterized by 50 % inhibition (IC50) of human breast cancer cell lines (MCF-7) using 3-(4,5-dimethylthaizol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Apoptosis was analysed by Hoechst33258 staining and DNA ladder. MCF-7 cellular superoxide dismutase (SOD), catalase (CAT) vitality and malondialdehyde (MDA) content were evaluated.Results: The essential oil was cytotoxic to MCF-7 cell line. A dose- and time-dependent inhibition was observed with IC50 values of 18.75, 9.45 and 10.50 ÎŒg/ml at 6, 24 and 48 h, respectively. Analyses by Hoechst33258 staining and DNA ladder indicate that the essential oil induced apoptosis. SOD vitality significantly decreased (pïŒ 0.05) by 51 % when the concentration of the essential oil increased from 1.25 to 12.5 ÎŒg/ml while CAT vitality significantly increased (p ïŒ 0.05) by 71 % when essential oil concentration was similarly increased. The MDA content of each treatment group, when compare to control, did not show any significant difference (p ïŒ 0.05).Conclusion: The essential oil of C. ambrosioides was cytotoxic to MCF-7 cell line and induced apoptosis.Keywords: Chenopodium ambrosioides L., Essential oil, Cytotoxicity, Apoptosis, Breast cancer, MCF-7 cells
Electric field induced cis-to-trans isomerization of polyphenylacetylene in solid state
A field induced isomerization from cis to trans form in
stereoregular cis-rich polyphenylacetylenes (PPAs) was
found, and it provides an alternate method to control the
order of chromophores in thin solid films
Performance of a dipstick dye immunoassay for rapid screening of Schistosoma japonicum infection in areas of low endemicity
BACKGROUND: The dipstick dye immunoassay (DDIA), recently commercially available in the People's Republic of China (P.R. China), is a rapid and simple test to detect human antibodies against Schistosoma Japonicum. Its performance and utility for screening schistosome infection in low endemic areas is little known. We therefore carried out a cross-sectional survey in seven villages with low endemicity of schistosomiasis in P.R. China and assessed the performance and utility of DDIA for diagnosis of schistosomiasis. Stool samples were collected and examined by the Kato-Katz method and the miracidium hatching technique. Serum samples, separated from whole blood of participants, were tested by DDIA. RESULTS: 6285 individuals aged 6-65 years old participated in this study, with a prevalence of schistosomiasis of 4.20%. Using stool examination as a gold reference standard, DDIA performed with a high overall sensitivity of 91.29% (95% CI: 87.89-94.69%) and also a high negative predictive value, with a mean value of 99.29% (95% CI: 98.99-99.58%). The specificity of DDIA was only moderate (53.08%, 95% CI: 51.82-54.34%). Multivariate analysis indicated that age, occupation and history of schistosome infection were significantly associated with the false positive results of DDIA. CONCLUSIONS: DDIA is a sensitive, rapid, simple and portable diagnostic assay and can be used as a primary approach for screening schistosome infection in areas of low endemicity. However, more sensitive and specific confirmatory assays need to be developed and combined with DDIA for targeting chemotherapy accurately
Mass Density Perturbations from Inflation with Thermal Dissipation
We study the power spectrum of the mass density perturbations in an inflation
scenario that includes thermal dissipation. We show that the condition on which
the thermal fluctuations dominate the primordial density perturbations can
easily be realized even for weak dissipation, i.e., the rate of dissipation is
less than the Hubble expansion. We find that our spectrum of primordial density
perturbations follows a power law behavior, and exhibits a ``thermodynamical''
feature -- the amplitude and power index of the spectrum depend mainly on the
thermodynamical variable , the inflation energy scale. Comparing this result
with the observed temperature fluctuations of the cosmic microwave background,
we find that both amplitude and index of the power spectrum can be fairly well
fitted if GeV.Comment: 23 pages, 7 figures, REVTex; Phys. Rev. D in pres
Discovery of a radio lobe in the Cloverleaf Quasar at z = 2.56
The fast growth of supermassive black holes and their feedback to the host
galaxies play an important role in regulating the evolution of galaxies,
especially in the early Universe. However, due to cosmological dimming and the
limited angular resolution of most observations, it is difficult to resolve the
feedback from the active galactic nuclei (AGN) to their host galaxies.
Gravitational lensing, for its magnification, provides a powerful tool to
spatially differentiate emission originated from AGN and host galaxy at high
redshifts. Here we report a discovery of a radio lobe in a strongly lensed
starburst quasar, H1413+117 or Cloverleaf at redshift , based on
observational data at optical, sub-millimetre, and radio wavelengths. With both
parametric and non-parametric lens models and with reconstructed images on the
source plane, we find a differentially lensed, kpc scaled, single-sided radio
lobe, located at to the north west of the host galaxy
on the source plane. From the spectral energy distribution in radio bands, we
find that the radio lobe has an energy turning point residing between 1.5 GHz
and 8 GHz, indicating an age of 20--50 Myr. This could indicate a feedback
switching of Cloverleaf quasar from the jet mode to the quasar mode
Triggered Star Formation in the Orion Bright-Rimmed Clouds
We have developed an empirical and effective set of criteria, based on the
2MASS colors, to select candidate classical T Tauri stars (CTTS). This provides
a useful tool to study the young stellar population in star-forming regions.
Here we present our analysis of the bright-rimmed clouds (BRCs) B 35, B 30, IC
2118, LDN 1616, LDN 1634, and Orion East to show how massive stars interact
with molecular clouds to trigger star formation. Our results support the
radiation-driven implosion model in which the ionization fronts from OB stars
compress a nearby cloud until the local density exceeds the critical value,
thereby inducing the cloud to collapse to form stars. We find that only BRCs
associated with strong IRAS 100 micron emission (tracer of high density) and
H-alpha emission (tracer of ionization fronts) show signs of ongoing star
formation. Relevant timescales, including the ages of O stars, expanding HII
regions, and the ages of CTTS, are consistent with sequential star formation.
We also find that CTTS are only seen between the OB stars and the BRCs, with
those closer to the BRCs being progressively younger. There are no CTTS leading
the ionization fronts, i.e., within the molecular clouds. All these provide
strong evidence of triggered star formation and show the major roles massive
stars play in sustaining the star-forming activities in the region.Comment: To appear in Ap
An Attempt to Determine the Largest Scale of Primordial Density Perturbations in the Universe
Inflationary cosmology predicts that the particle horizon should be
generically much bigger than the present-day Hubble radius, . This
implies a special regime of super-Hubble scale energy density fluctuations
imprinted on the cosmic microwave background radiation (CMBR), which from
present theory could only be explained by inflation Causality constraints are
used to determine models for the power spectrum that accommodate a suppression
scale. A three parameter likelihood analysis is performed of the COBE-DMR
4-year data with respect to the amplitude, spectral index, and suppression
scale. It is found that all suppression length scales larger than are
consistent with the data, but that scales of order are slightly
preferred, at roughly the one-sigma level. Many non-inflation models would be
consistent with a small suppression length scale, whereas for standard
inflation models, the duration of the inflation epoch would have to be bounded
by a fairly small upper limit. Suppression scales smaller than are
strongly excluded by the anisotrophy data.Comment: 9 pages, Latex, 1 figure, additional tests reporte
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