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$\ \textrm{mV}/\Phi_0$) and flux-to-current (above 12$\ \textrm{nA}/\Phi_0$) transfer functions, with the best estimated flux sensitivity $\sim$2.6$\ \mu\Phi_0/\sqrt{\textrm{Hz}}$ reached under fixed voltage bias, where $\Phi_0$ is the flux quantum. The interferometers operate up to $T_\textrm{bath}\simeq$ 2 $\textrm{K}$, 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

0-π\pi phase-controllable thermalthermal Josephson junction

Two superconductors coupled by a weak link support an equilibrium Josephson electrical current which depends on the phase difference $\varphi$ between the superconducting condensates [1]. Yet, when a temperature gradient is imposed across the junction, the Josephson effect manifests itself through a coherent component of the heat current that flows oppositely to the thermal gradient for $\varphi <\pi/2$ [2-4]. The direction of both the Josephson charge and heat currents can be inverted by adding a $\pi$ shift to $\varphi$. In the static electrical case, this effect was obtained in a few systems, e.g. via a ferromagnetic coupling [5,6] or a non-equilibrium distribution in the weak link [7]. These structures opened new possibilities for superconducting quantum logic [6,8] and ultralow power superconducting computers [9]. Here, we report the first experimental realization of a thermal Josephson junction whose phase bias can be controlled from $0$ to $\pi$. This is obtained thanks to a superconducting quantum interferometer that allows to fully control the direction of the coherent energy transfer through the junction [10]. This possibility, joined to the completely superconducting nature of our system, provides temperature modulations with unprecedented amplitude of $\sim$ 100 mK and transfer coefficients exceeding 1 K per flux quantum at 25 mK. Then, this quantum structure represents a fundamental step towards the realization of caloritronic logic components, such as thermal transistors, switches and memory devices [10,11]. These elements, combined with heat interferometers [3,4,12] and diodes [13,14], would complete the thermal conversion of the most important phase-coherent electronic devices and benefit cryogenic microcircuits requiring energy management, such as quantum computing architectures and radiation sensors.Comment: 10 pages, 9 color figure