13,686 research outputs found
Pseudo-gap features of intrinsic tunneling in (HgBr_2)-Bi2212 single crystals
The c-axis tunneling properties of both pristine Bi2212 and its HgBr
intercalate have been measured in the temperature range 4.2 - 250 K.
Lithographically patterned 7-10 unit-cell heigh mesa structures on the surfaces
of these single crystals were investigated. Clear SIS-like tunneling curves for
current applied in the -axis direction have been observed. The dynamic
conductance dd shows both sharp peaks corresponding to a
superconducting gap edge and a dip feature beyond the gap, followed by a wide
maximum, which persists up to a room temperature. Shape of the temperature
dependence of the {\it c}-axis resistance does not change after the
intercalation suggesting that a coupling between -bilayers has
little effect on the pseudogap.Comment: 6 pages, 5 figures; presented at the Second Int Conf. New3Sc-1999
(Las Vegas, NV
Heavy Grazing Significantly Reduced the Temporal Stability of Aboveground Biomass
The stability of a plant community is the embodiment of the dynamic balance achieved by the interaction between populations in the form of competition or mutual benefit. Temporal stability refers to the ratio of the average value to the variance of the biomass of the population or community. For grassland ecosystems, the stability of the grassland plant community is the basis for its survival and functional performance, and is the key factor affecting its structure and function. In order to study the impact of grazing on the temporal stability of aboveground biomass of desert steppe, this study used a completely randomized block design to study the relationship between the temporal stability of Stipa breviflora desert steppe vegetation communities and functional groups under different grazing intensities and their influencing factors, and then explored the relationship between temporal stability and species richness and species asynchrony. The results showed that heavy grazing significantly reduced temporal stability, species richness and species asynchrony of grassland communities. In terms of plant functional groups, grazing significantly reduced the stability of shrubs, semi-shrubs and perennial miscellaneous grasses. There were significant positive correlations between species richness and species asynchrony and community stability. Therefore, understanding changes in community asynchrony, richness and functional group stability is of great significance to further understanding of the temporal stability of desert grassland plant communities
Decay of weak solutions to the 2D dissipative quasi-geostrophic equation
We address the decay of the norm of weak solutions to the 2D dissipative
quasi-geostrophic equation. When the initial data is in only, we prove
that the norm tends to zero but with no uniform rate, that is, there are
solutions with arbitrarily slow decay. For the initial data in ,
with , we are able to obtain a uniform decay rate in . We
also prove that when the norm of the initial data
is small enough, the norms, for have uniform
decay rates. This result allows us to prove decay for the norms, for , when the initial data is in .Comment: A paragraph describing work by Carrillo and Ferreira proving results
directly related to the ones in this paper is added in the Introduction. Rest
of the article remains unchange
Spatially and Spectrally Resolved Observations of a Zebra Pattern in Solar Decimetric Radio Burst
We present the first interferometric observation of a zebra-pattern radio
burst with simultaneous high spectral (~ 1 MHz) and high time (20 ms)
resolution. The Frequency-Agile Solar Radiotelescope (FASR) Subsystem Testbed
(FST) and the Owens Valley Solar Array (OVSA) were used in parallel to observe
the X1.5 flare on 14 December 2006. By using OVSA to calibrate the FST the
source position of the zebra pattern can be located on the solar disk. With the
help of multi-wavelength observations and a nonlinear force-free field (NLFFF)
extrapolation, the zebra source is explored in relation to the magnetic field
configuration. New constraints are placed on the source size and position as a
function of frequency and time. We conclude that the zebra burst is consistent
with a double-plasma resonance (DPR) model in which the radio emission occurs
in resonance layers where the upper hybrid frequency is harmonically related to
the electron cyclotron frequency in a coronal magnetic loop.Comment: Accepted for publication in Ap
On the global well-posedness of a class of Boussinesq- Navier-Stokes systems
In this paper we consider the following 2D Boussinesq-Navier-Stokes systems
\partial_{t}u+u\cdot\nabla u+\nabla p+ |D|^{\alpha}u &= \theta e_{2}
\partial_{t}\theta+u\cdot\nabla \theta+ |D|^{\beta}\theta &=0 \quad with
and . When , , where is an explicit function
as a technical bound, we prove global well-posedness results for rough initial
data.Comment: 23page
Infrared conductivity of hole accumulation and depletion layers in (Ga,Mn)As- and (Ga,Be)As-based electric field-effect devices
We have fabricated electric double-layer field-effect devices to
electrostatically dope our active materials, either =0.015
GaMnAs or =3.2 GaBeAs. The devices
are tailored for interrogation of electric field induced changes to the
frequency dependent conductivity in the accumulation or depletions layers of
the active material via infrared (IR) spectroscopy. The spectra of the
(Ga,Be)As-based device reveal electric field induced changes to the IR
conductivity consistent with an enhancement or reduction of the Drude response
in the accumulation and depletion polarities, respectively. The spectroscopic
features of this device are all indicative of metallic conduction within the
GaAs host valence band (VB). For the (Ga,Mn)As-based device, the spectra show
enhancement of the far-IR itinerant carrier response and broad mid-IR resonance
upon hole accumulation, with a decrease of these features in the depletion
polarity. These later spectral features demonstrate that conduction in
ferromagnetic (FM) GaMnAs is distinct from genuine metallic
behavior due to extended states in the host VB. Furthermore, these data support
the notion that a Mn-induced impurity band plays a vital role in the electron
dynamics of FM GaMnAs. We add, a sum-rule analysis of the spectra
of our devices suggests that the Mn or Be doping does not lead to a substantial
renormalization of the GaAs host VB
Apoptosome activation, an important molecular instigator in 6-mercaptopurine induced Leydig cell death.
Leydig cells are crucial to the production of testosterone in males. It is unknown if the cancer chemotherapeutic drug, 6-mercaptopurine (6 MP), produces Leydig cell failure among adult survivors of childhood acute lymphoblastic leukemia. Moreover, it is not known whether Leydig cell failure is due to either a loss of cells or an impairment in their function. Herein, we show, in a subset of childhood cancer survivors, that Leydig cell failure is related to the dose of 6 MP. This was extended, in a murine model, to demonstrate that 6 MP exposure induced caspase 3 activation, and the loss of Leydig cells was independent of Bak and Bax activation. The death of these non-proliferating cells was triggered by 6 MP metabolism, requiring formation of both cytosolic reactive oxygen species and thiopurine nucleotide triphosphates. The thiopurine nucleotide triphosphates (with physiological amounts of dATP) uniquely activated the apoptosome. An ABC transporter (Abcc4/Mrp4) reduced the amount of thiopurines, thereby providing protection for Leydig cells. The studies reported here demonstrate that the apoptosome is uniquely activated by thiopurine nucleotides and suggest that 6 MP induced Leydig cell death is likely a cause of Leydig cell failure in some survivors of childhood cancer
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