162 research outputs found
On-Chip Cooling by Heating with Superconducting Tunnel Junctions
Heat management and refrigeration are key concepts for nanoscale devices
operating at cryogenic temperatures. The design of an on-chip mesoscopic
refrigerator that works thanks to the input heat is presented, thus realizing a
solid state implementation of the concept of cooling by heating. The system
consists of a circuit featuring a thermoelectric element based on a
ferromagnetic insulator-superconductor tunnel junction (N-FI-S) and a series of
two normal metal-superconductor tunnel junctions (SINIS). The N-FI-S element
converts the incoming heat in a thermovoltage, which is applied to the SINIS,
thereby yielding cooling. The cooler's performance is investigated as a
function of the input heat current for different bath temperatures. We show
that this system can efficiently employ the performance of SINIS refrigeration,
with a substantial cooling of the normal metal island. Its scalability and
simplicity in the design makes it a promising building block for
low-temperature on-chip energy management applications.Comment: 7 pages, 6 figure
Climate Change and Extreme Events: an Assessment of Economic Implications
We use a general equilibrium model of the world economy, and a regional economic growth model, to assess the economic implications of vulnerability from extreme meteorological events, induced by the climate change. In particular, we first consider the impact of climate change on ENSO and NAO oceanic oscillations and, subsequently, the implied variation on regional expected damages. We found that expected damages from extreme events are increasing in the United States, Europe and Russia, and decreasing in energy exporting countries. Two economic implications are taken into account: (1) short-term impacts, due to changes in the demand structure, generated by higher/lower precautionary saving, and (2) variations in regional economic growth paths. We found that indirect stort-term effects(variations in savings due to higher or lower likelihood of natural disasters) can have an impact on regional economies, whose order of magnitude is comparable to the one of direct damages. On the other hand, we highlight that higher vulnerability from extreme events translates into higher volatility in the economic growth path, and vice versa.Climate Change, Extreme Events, Computable General Equilibrium Models, Precautionary Savings, Economic Growth
Short term ozone effects on morbidity for the city of Milano, Italy, 1996-2003.
In this paper, we explore a range of concerns that arise in measuring short term ozone effects on health. In particular, we tackle the problem of measuring exposure using alternative daily measures of ozone derived from hourly concentrations. We adopt the exposure paradigm of Chiogna and Bellini (2002), and we compare its performances with respect to traditional exposure measures by exploiting model selection. For investigating model selection stability issues, we then apply the idea of bootstrapping the modelling process
Analysis of heat waves effects on health using GAM and bootstrap based model selection.
It is known that high summer temperature may lead to worsening health conditions among fragile individuals within exposed populations. It is also argued that multi-day patterns of high temperature – heat waves – may have relevant effects on health. We will discuss the possible measures of heat waves intensity to be included in a generalized additive model explaining the number of hospital admissions occurred during summer months in Milano. The issue of variable selection is central to the analysis: a computational method is discussed which may help in assessing the robustness of model selection method. Eventually, we obtain evidence supporting the relevance of heat waves in driving adverse health episodes
High operating temperature in V-based superconducting quantum interference proximity transistors
Here we report the fabrication and characterization of fully superconducting
quantum interference proximity transistors (SQUIPTs) based on the
implementation of vanadium (V) in the superconducting loop. At low temperature,
the devices show high flux-to-voltage (up to 0.52) and
flux-to-current (above 12) transfer functions, with the
best estimated flux sensitivity 2.6
reached under fixed voltage bias, where is the flux quantum. The
interferometers operate up to 2 , with an
improvement of 70 of the maximal operating temperature with respect to
early SQUIPTs design. The main features of the V-based SQUIPT are described
within a simplified theoretical model. Our results open the way to the
realization of SQUIPTs that take advantage of the use of higher-gap
superconductors for ultra-sensitive nanoscale applications that operate at
temperatures well above 1 K.Comment: Published version with Supplementary Informatio
Phase-driven collapse of the Cooper condensate in a nanosized superconductor
Superconductivity can be understood in terms of a phase transition from an
uncorrelated electron gas to a condensate of Cooper pairs in which the relative
phases of the constituent electrons are coherent over macroscopic length
scales. The degree of correlation is quantified by a complex-valued order
parameter, whose amplitude is proportional to the strength of the pairing
potential in the condensate. Supercurrent-carrying states are associated with
non-zero values of the spatial gradient of the phase. The pairing potential and
several physical observables of the Cooper condensate can be manipulated by
means of temperature, current bias, dishomogeneities in the chemical
composition or application of a magnetic field. Here we show evidence of
complete suppression of the energy gap in the local density of quasiparticle
states (DOS) of a superconducting nanowire upon establishing a phase difference
equal to pi over a length scale comparable to the superconducting coherence
length. These observations are consistent with a complete collapse of the
pairing potential in the center of the wire, in accordance with theoretical
modeling based on the quasiclassical theory of superconductivity in diffusive
systems. Our spectroscopic data, fully exploring the phase-biased states of the
condensate, highlight the profound effect that extreme phase gradients exert on
the amplitude of the pairing potential. Moreover, the sharp magnetic response
observed near the onset of the superconducting gap collapse regime can be
exploited to realize ultra-low noise magnetic flux detectors.Comment: 7 pages, 5 color figures plus supporting inf
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