986 research outputs found
A one-compartment, direct glucose fuel cell for powering long-term medical implants
We present the operational concept, microfabrication, and electrical performance of an enzyme-less direct glucose fuel cell for harvesting the chemical energy of glucose from body fluids. The spatial concentrations of glucose and oxygen at the electrodes of the one-compartment setup are established by self-organization, governed by the balance of electro-chemical depletion and membrane diffusion. Compared to less stable enzymatic and immunogenic microbial fuel cells, this robust approach excels with an extended life time, the amenability to sterilization and biocompatibility, showing up a clear route towards an autonomous power supply for long-term medical implants without the need of surgical replacement and external refueling. Operating in physiological phosphate buffer solution containing 0.1 wt% glucose and having a geometrical cathode area of 10 cm2, our prototype already delivers 20 ” W peak power over a period of 7 days
Exact Analysis of Soliton Dynamics in Spinor Bose-Einstein Condensates
We propose an integrable model of a multicomponent spinor Bose-Einstein
condensate in one dimension, which allows an exact description of the dynamics
of bright solitons with spin degrees of freedom. We consider specifically an
atomic condensate in the F=1 hyperfine state confined by an optical dipole
trap. When the mean-field interaction is attractive (c_0 < 0) and the
spin-exchange interaction of a spinor condensate is ferromagnetic (c_2 < 0), we
prove that the system possesses a completely integrable point leading to the
existence of multiple bright solitons. By applying results from the inverse
scattering method, we analyze a collision law for two-soliton solutions and
find that the dynamics can be explained in terms of the spin precession.Comment: 4 pages, 2 figure
Predominantly Superconducting Origin of Large Energy Gaps in Underdoped Bi2Sr2CaCu2O8-d from Tunneling Spectroscopy
New tunneling data are reported in underdoped Bi2Sr2CaCu2O8-d using
superconductor-insulator-superconductor break junctions. Energy gaps, Delta, of
51+2, 54+2 and 57+3 meV are observed for three crystals with Tc=77, 74, and 70
K respectively. These energy gaps are nearly three times larger than for
overdoped crystals with similar Tc. Detailed examination of tunneling spectra
over a wide doping range from underdoped to overdoped, including the Josephson
IcRn product, indicate that these energy gaps are predominantly of
superconducting origin.Comment: 10 pages, 4 figures, 1 tabl
Multiple deleted regions on the long arm of chromosome 6 in astrocytic tumours
Chromosome 6 deletions are common in human neoplasms including gliomas. In order to study the frequency and identify commonly deleted regions of chromosome 6 in astrocytomas, 159 tumours (106 glioblastomas, 39 anaplastic astrocytomas and 14 astrocytomas malignancy grade II) were analysed using 31 microsatellite markers that span the chromosome. Ninety-five per cent of cases with allelic losses had losses affecting 6q. Allelic losses were infrequent in astrocytomas malignancy grade II (14%) but more usual in anaplastic astrocytomas (38%) and glioblastomas (37%). Evidence for clonal heterogeneity in the astrocytomas and anaplastic astrocytomas was frequently observed (i.e. co-existence of subpopulations with and without chromosome 6 deletions). Clonal heterogeneity was less common in glioblastomas. Five commonly deleted regions were identified on 6q. These observations suggest that a number of tumour suppressor genes are located on 6q and that these genes may be involved in the progression of astrocytic tumours. © 2000 Cancer Research Campaig
Pairing Fluctuation Theory of Superconducting Properties in Underdoped to Overdoped Cuprates
We propose a theoretical description of the superconducting state of under-
to overdoped cuprates, based on the short coherence length of these materials
and the associated strong pairing fluctuations. The calculated and the
zero temperature excitation gap , as a function of hole
concentration , are in semi-quantitative agreement with experiment. Although
the ratio has a strong dependence, different from the
universal BCS value, and deviates significantly from the BCS
prediction, we obtain, quite remarkably, quasi-universal behavior, for the
normalized superfluid density and the Josephson critical
current , as a function of . While experiments on
are consistent with these results, future measurements on
are needed to test this prediction.Comment: 4 pages, 3 figures, REVTeX, submitted to Phys. Rev. Let
dc readout experiment at the Caltech 40m prototype interferometer
The Laser Interferometer Gravitational Wave Observatory (LIGO) operates a 40m prototype interferometer on the Caltech campus. The primary mission of the prototype is to serve as an experimental testbed for upgrades to the LIGO interferometers and for gaining experience with advanced interferometric techniques, including detuned resonant sideband extraction (i.e. signal recycling) and dc readout (optical homodyne detection). The former technique will be employed in Advanced LIGO, and the latter in both Enhanced and Advanced LIGO. Using dc readout for gravitational wave signal extraction has several technical advantages, including reduced laser and oscillator noise couplings as well as reduced shot noise, when compared to the traditional rf readout technique (optical heterodyne detection) currently in use in large-scale ground-based interferometric gravitational wave detectors. The Caltech 40m laboratory is currently prototyping a dc readout system for a fully suspended interferometric gravitational wave detector. The system includes an optical filter cavity at the interferometer's output port, and the associated controls and optics to ensure that the filter cavity is optimally coupled to the interferometer. We present the results of measurements to characterize noise couplings in rf and dc readout using this system
Possible Universal Cause of High-T_c Superconductivity in Different Metals
Using the theory of the high temperature superconductivity based on the idea
of the fermion condensation quantum phase transition (FCQPT), we show that
neither the d-wave pairing symmetry, nor the pseudogap phenomenon, nor the
presence of the Cu-O_2 planes are of decisive importance for the existence of
the high-T_c superconductivity. We analyze recent experimental data on this
type of superconductivity in different materials and show that these facts can
be understood within the theory of superconductivity based on FCQPT. The latter
can be considered as a universal cause of the high-T_c superconductivity. The
main features of a room-temperature superconductor are discussed.Comment: 8 pages, Revtex, revised and accepted by JETP Letter
Avaliação sorológica de vacinas comerciais polivalentes contra a enterotoxemia em caprinos.
Foram avaliadas as respostas sorolĂłgicas a cinco vacinas comerciais polivalentes que continham o toxĂłide Ă©psilon do Clostridium perfringens tipo D na sua formulação. Para isso, foram utilizados 84 caprinos jovens, divididos aleatoriamente em seis grupos experimentais com 14 animais em cada grupo. Os caprinos do Grupo Controle nĂŁo receberam nenhuma dose de vacina e os dos Grupos 1 ao 5 receberam duas doses de vacina com intervalo de quatro semanas entre elas. A primeira dose de vacina foi aplicada aos 45 (± 3) dias de vida dos animais (inĂcio do experimento - dia zero) e a segunda aos 75 (± 3 ? dia 30). As amostras de sangue para a realização dos testes sorolĂłgicos foram colhidas antes (dia zero), e nos dias 30, 60, 90, 120 e 150 apĂłs o inĂcio do experimento. Utilizou-se a tĂ©cnica de ELISA Indireto para quantificação dos anticorpos antitoxina Ă©psilon do C. perfringens tipo D. De maneira geral ocorreu um aumento nos valores mĂ©dios do tĂtulo de anticorpos sĂ©ricos dos caprinos no dia 60 em resposta Ă s duas doses de vacina recebidas nos dias zero e 30, sendo que o maior nĂșmero de animais considerados protegidos tambĂ©m foi detectado neste dia. Apenas cinco caprinos jovens do Grupo 1 e um do Grupo 3 permaneceram com tĂtulos de anticorpos considerados protetores atĂ© o dia 150. Diante dos resultados obtidos, concluiu-se que as vacinas avaliadas apresentaram baixa capacidade de estimular uma resposta imune protetora nos caprinos avaliados
Phenomenology of Photoemission Lineshapes of High Tc Superconductors
We introduce a simple phenomenological form for the self-energy which allows
us to extract important information from angle resolved photoemission data on
the high Tc superconductor Bi2212. First, we find a rapid suppression of the
single particle scattering rate below Tc for all doping levels. Second, we find
that in the overdoped materials the gap Delta at all k-points on the Fermi
surface has significant temperature dependence and vanishes near Tc. In
contrast, in the underdoped samples such behavior is found only at k-points
close to the diagonal. Near (pi,0), Delta is essentially T-independent in the
underdoped samples. The filling-in of the pseudogap with increasing T is
described by a broadening proportional to T-Tc, which is naturally explained by
pairing correlations above Tc.Comment: 4 pages, revtex, 3 encapsulated postscript figure
Possible pseudogap behavior of electron doped high-temperature superconductors
We have measured the low-energy quasiparticle excitation spectrum of the
electron doped high-temperature superconductors (HTS) Nd(1.85)Ce(0.15)CuO(4-y)
and Pr(1.85)Ce(0.15)CuO(4-y) as a function of temperature and applied magnetic
field using tunneling spectroscopy. At zero magnetic field, for these optimum
doped samples no excitation gap is observed in the tunneling spectra above the
transition temperature Tc. In contrast, below Tc for applied magnetic fields
well above the resistively determined upper critical field, a clear excitation
gap at the Fermi level is found which is comparable to the superconducting
energy gap below Tc. Possible interpretations of this observation are the
existence of a normal state pseudogap in the electron doped HTS or the
existence of a spatially non-uniform superconducting state.Comment: 4 pages, 4 ps-figures included, to be published in Phys. Rev. B,
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