587 research outputs found
Efficient Peltier refrigeration by a pair of normal metal/ insulator/superconductor junctions
We suggest and demonstrate in experiment that two normal metal /insulator/
superconductor (NIS) tunnel junctions combined in series to form a symmetric
SINIS structure can operate as an efficient Peltier refrigerator. Specifically,
it is shown that the SINIS structure with normal-state junction resistances 1.0
and 1.1 k is capable of reaching a temperature of about 100 mK starting
from 300 mK. We estimate the corresponding cooling power to be 1.5 pW per total
junction area of 0.8 m at mK.Comment: 7 pages, revtex, 3 figures by fax/conventional mail upon reques
An NTCP Analysis of Urethral Complications from Low Doserate Mono- and Bi-Radionuclide Brachytherapy
Urethral NTCP has been determined for three prostates implanted with seeds based on 125I (145 Gy), 103Pd (125 Gy), 131Cs (115 Gy), 103Pd-125I (145 Gy), or 103Pd-131Cs (115 Gy or 130 Gy).
First, DU20, meaning that 20% of the urhral volume receive a dose of at least DU20, is converted into an I-125 LDR equivalent DU20 in order to use the urethral NTCP model.
Second, the propagation of uncertainties through the steps in the NTCP calculation was assessed in order to identify the parameters responsible for large data uncertainties. Two sets of radiobiological parameters were studied. The NTCP results all fall in the 19%–23% range and are associated with large uncertainties, making the comparison difficult. Depending on the dataset chosen, the ranking of NTCP values among the six seed implants studied changes. Moreover, the large uncertainties on the fitting parameters of the urethral NTCP model result in large uncertainty on the NTCP value. In conclusion, the use of NTCP model for permanent brachytherapy is feasible but it is essential that the uncertainties on the parameters in the model be reduced
Qualidade do requeijão cremoso de leite de búfalas suplementadas com subprodutos agroindustriais, em Belém, Pará.
Objetivou-se avaliar o requeijão cremoso de leite de búfalas suplementadas com concentrados proteicos, T1 (controle): farelo de milho e soja, T2: farelo de milho e soja e torta de cupuaçu (Theobroma grandiflorum), e T3: farelo de milho e soja e torta de murumuru (Astrocaryum murumuru), em três repetições. Os animais são provenientes do rebanho experimental da Unidade de Pesquisa "Dr. Felisberto Camargo" (01º28'S e 48º27'W), Belém, Pará, da Embrapa Amazônia Oriental. Foram realizadas análises físico-químicas, microbiológicas e sensoriais, a fim de detectar diferenças na utilização de leite oriundo de diferentes dietas alimentares. A composição nutricional dos derivados lácteos não resultou em diferenças signi cativas (p<0,05), o que indica que a produção de leite é viável com uso de rações onde há substituição parcial da soja e milho, por ingredientes de baixo custo, constituídos por subprodutos da agroindústria, além de evitar que sejam descartados no ambiente. Os derivados elaborados atenderam aos padrões higiênico-sanitários preconizados pela legislação vigente. Quanto à aceitação sensorial, houve diferença significativa entre os tratamentos e os derivados foram bem aceitos, o que indica sua viabilidade de produção, de baixo custo (R$ 1,43/100 g). Dessa forma, a suplementação alimentar com resíduos agroindustriais pode incentivar a pecuária bubalina leiteira, gerar emprego e renda na pequena propriedade e possibilitar o desenvolvimento da cadeia produtiva
Non Equilibrium Electronic Distribution in Single Electron Devices
The electronic distribution in devices with sufficiently small diemnsions may
not be in thermal equilibrium with their surroundings. Systems where the
occupancies of electronic states are solely determined by tunneling processes
are analyzed. It is shown that the effective temperature of the device may be
higher, or lower, than that of its environment, depending on the applied
voltage and the energy dependence of the tunneling rates. The I-V
characteristics become asymmetric. Comparison with recent experiments is made
Thermopower of a single electron transistor in the regime of strong inelastic cotunneling
We study Coulomb blockade oscillations of thermoelectric coefficients of a
single electron transistor based on a quantum dot strongly coupled to one of
the leads by a quantum point contact. At temperatures below the charging energy
E_C the transport of electrons is dominated by strong inelastic cotunneling. In
this regime we find analytic expressions for the thermopower as a function of
temperature T and the reflection amplitude in the contact. In the case when
the electron spins are polarized by a strong external magnetic field, the
thermopower shows sinusoidal oscillations as a function of the gate voltage
with the amplitude of the order of . We obtain
qualitatively different results in the absence of the magnetic field. At
temperatures between and the thermopower oscillations are
sinusoidal with the amplitude of order . On the
other hand, at we find non-sinusoidal oscillations of the
thermopower with the amplitude .Comment: 14 pages, 3 figure
Dissipationless BCS Dynamics with Large Branch Imbalance
In many situations a BCS-type superconductor will develop an imbalance
between the populations of the holelike and electronlike spectral branches.
This imbalance suppresses the gap. It has been noted by Gal'perin et al. [Sov.
Phys. JETP 54, 1126 (1981)] that at large imbalance, when the gap is
substantially suppressed, an instability develops. The analytic treatment of
the system beyond the instability point is complicated by the fact that the
Boltzmann approach breaks down. We study the short-time behavior following the
instability, in the collisionless regime, using methods developed by Yuzbashyan
et al. [J. Phys. A 38, 7831 (2005); Phys. Rev. B 72, 220503(R) (2005)].Comment: 12 pages, 3 figure
Experimental Implementation of a Two-Stroke Quantum Heat Engine
We put forth an experimental simulation of a stroboscopic two-stroke thermal
engine in the IBMQ processor. The system consists of a quantum spin chain
connected to two baths at their boundaries, prepared at different temperatures
using the variational quantum thermalizer algorithm. The dynamics alternates
between heat and work strokes, which can be separately designed using
independent quantum circuits. The results show good agreement with theoretical
predictions, showcasing IBMQ as a powerful tool to study thermodynamics in the
quantum regime, as well as the implementation of variational quantum algorithms
in real-world quantum computers. It also opens the possibility of simulating
quantum heat transport across a broad range of chains geometries and
interactions
Well-being, work comfort and food security are better than maximizing production in the Amazon.
In the Amazon, slash and burn is the most common technique used by American-Indians, small farmers and even big ranches to transform forests into rural landscapes. The basis of food subsistence for diverse populations (rice, corn and bean), slash and burn is also a must for the plantation of cocoa, coffee, palms and pastures. The Amazonian rural landscape is currently dominated by pastures, occupying around 80 % of the deforested surface. Even if the nature of the plantation varies according to location, height, soil type and local traditions, slash and burn remains relatively the same in all regions. Agro-ecological intensification and the integration of livestock and agriculture is 2-3 decades old. Different alternatives have been tested, particularly the introduction of leguminous (covering the land or forming trees) to improve the soil and to build a bank of proteins for cattle. New techniques for the recuperation of pasture lands have become widely popular among ranches. The introduction of one or two annual plantations between two pasture areas allows reestablishing fertility through the injection of nitrates and, as a result, increases the pasture?s productivity. However, being relatively high-cost because of its demand in terms of mechanization and inputs, this technique is almost unaffordable for small Amazonian farmers..
Norepinephrine Triggers Metaplasticity of LTP by Increasing Translation of Specific mRNAs
Norepinephrine (NE) is a key modulator of synaptic plasticity in the hippocampus, a brain structure crucially involved in memory formation. NE boosts synaptic plasticity mostly through initiation of signaling cascades downstream from beta (β)-adrenergic receptors (β-ARs). Previous studies demonstrated that a β-adrenergic receptor agonist, isoproterenol, can modify the threshold for long-term potentiation (LTP), a putative cellular mechanism for learning and memory, in a process known as “metaplasticity.” Metaplasticity is the ability of synaptic plasticity to be modified by prior experience. We asked whether NE itself could engage metaplastic mechanisms in area CA1 of mouse hippocampal slices. Using extracellular field potential recording and stimulation, we show that application of NE (10 µM), which did not alter basal synaptic strength, enhances the future maintenance of LTP elicited by subthreshold, high-frequency stimulation (HFS: 1 × 100 Hz, 1 sec). HFS applied 30 min after NE washout induced long-lasting (>4 h) LTP, which was significantly extended in duration relative to HFS alone. This NE-induced metaplasticity required β1-AR activation, as coapplication of the β1-receptor antagonist CGP-20712A (1 µM) attenuated maintenance of LTP. We also found that NE-mediated metaplasticity was translation- and transcription-dependent. Polysomal profiles of CA1 revealed increased translation rates for specific mRNAs during NE-induced metaplasticity. Thus, activation of β-ARs by NE primes synapses for future long-lasting plasticity on time scales extending beyond fast synaptic transmission; this may facilitate neural information processing and the subsequent formation of lasting memories
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