A cool spin on supercomputers

Niladri Banerjee explains how the emerging field of "superconducting spintronics" could lead to a new generation of green supercomputers that use far less energy than previous devices<br

Essays on Optimal Aid and Fiscal Policy in Developing Economies

Essay I: Which countries receive aid as insurance and why? A theory of optimal aid policy Empirical evidence shows that developing countries with opaque institutions receive procyclical Official Development Aid (ODA) while developing countries with transparent institutions receive acyclical or countercyclical ODA. This paper provides a dynamic equilibrium model of optimal aid policy that quantitatively accounts for this fact. In the model, the donor wants to (a) encourage actions by the aid receiving government that increase output and (b) smooth out economic fluctuations. The transparency of institutions in the country affects the donor's ability to distinguish downturns caused by exogenous shocks, from those caused by government actions. The solution to the donor's mechanism design problem is dependent on the transparency of government actions. If the donor has good information about government actions, aid policy is countercyclical and aid acts as insurance. However, if the donor is unable to infer perfectly the cause of the downturn, aid policy is procyclical to encourage unobservable good actions. The model predicts a similar pattern for ODA commitments for the following year which is supported by the data. For countries with opaque institutions procyclical aid is the result of optimal policies given the information constraints of donors. Essay II: New Evidence on the Relationship Between Aid Cyclicality and Institutions This paper documents a new fact: the correlation between official development assistance (ODA) and GDP is negatively related to the quality of institutions in the receipient country. Differences in institutional indicators that measure corruption, rule of law, government effectiveness and government transparency are particularly important. The results are robust to several modifications. The results hold for both pooled and within regressions specifications and for different sources of institutional quality measures. This fact also reconciles conflicting empirical results about the correlation between ODA and GDP in the literature. For instance, Pallage and Robe (2001) find a positive correlation in two thirds of African economies and half of non-African developing economies, but Rand and Tarp (2002) find no correlation in a different set of developing countries. First, once institutions are accounted for, African economies are not treated differently by donors. Second, the sample in Rand and Tarp (2002) comprises developing economies which have relatively good institutions, therefore, those countries receive acyclical or countercyclical aid. \\ Essay II: Optimal Procyclical Fiscal Policy Without Procyclical Government Spending Procyclical fiscal policy can be caused by either procyclical government expenditure, countercyclical taxes or both. The majority of models which try to explain procyclical fiscal policy as the result of optimal policy have procyclical government expenditures. This paper develops a model which optimally generates procyclical fiscal policy while keeping government expenditures acyclical. Instead, taxes are optimally countercyclical. The model uses endogenous sovereign default to generate an environment where interest rates are lower in booms than in recessions. If household's have insufficient access to financial instruments it is optimal for the government to lower taxes and borrow during booms. This enables impatient households to benefit from the lower interest rates in booms by helping the consumer bring consumption forward

Microfluidic device for triggered chip transience

pre-printThis paper presents the fabrication and testing of a microfluidic device for the triggered destruction (transience) of microchips. The device consists of a thin film array of sealed reservoirs patterned on a polymer film. Each reservoir encloses a corrosive chemical agent which upon release dissolves the surface of a microchip placed beneath. When transience is activated, an integrated micro-heater melts the bottom of the reservoirs thus releasing the chemical agent, which in a matter of minutes destroys key layers on the underlying electronic/sensor chip. Each reservoir consists of a 16 μm-tall cavity holding 1 μL/cm2 of 1000:1 BHF. The measured energy required to burst open a filled reservoir was ~35mJ/cm2 when the device rests on top of a glass substrate and ~100mJ/cm2 when the device rests on top of a 0.5 μm-layer of silicon dioxide on a 0.5 mm silicon wafer

Non-HIV AIDS presenting with adrenal histoplasmosis and pulmonary tuberculosis: a mesmerising case report and discussion

Non-HIV AIDS or idiopathic CD4 lymphocytopenia (ICL) is an acquired immunodeficiency syndrome resulting in CD4 lymphopenia without any evidence of HIV infection or any other apparent cause of immunosuppression.  A non-diabetic patient presented with adrenal histoplasmosis and UTI leading to adrenal failure. No immediate cause of immunosuppression was found, HIV, HTLV screening were negative. A CD4 count was done and the patient was found to be having non-HIV AIDS (idiopathic CD4 lymphocytopenia). He was treated and discharged. Few months later the patient presented again with adrenal failure & pulmonary tuberculosis. Adrenal FNAC showed persisting adrenal histoplasmosis. CD4 count found to be low again, but this time it was worse than the previous scenario

Magnetization reorientation due to the superconducting transition in heavy-metal heterostructures

Recent theoretical and experimental work has demonstrated how the superconducting critical temperature ($T_c$) can be modified by rotating the magnetization of a single homogeneous ferromagnet proximity-coupled to the superconducting layer. This occurs when the superconductor and ferromagnet are separated by a thin heavy normal metal that provides an enhanced interfacial Rashba spin-orbit interaction. We consider the reciprocal effect: magnetization reorientation driven by the superconducting phase transition. We solve the tight-binding Bogoliubov-de Gennes equations on a lattice self-consistently and find that the relative angle between the spin-orbit field and the magnetization gives rise to a contribution in the free energy even in the normal state due to band-structure effects. For temperatures below $T_c$, superconductivity gives rise to a competing contribution. By lowering the temperature, in addition to reorientation of the favored magnetization direction from in-plane to out-of-plane, a $\pi/4$ in-plane rotation for thicker ferromagnetic layers is possible. Furthermore, computation of $T_c$ of the structure in the ballistic limit shows a dependence on the in-plane orientation of the magnetization, in contrast to our previous result on the diffusive limit. This finding is relevant with respect to thin-film heterostructures since these are likely to be in the ballistic regime of transport. Finally, we discuss the experimental feasibility of observing the magnetic anisotropy induced by the superconducting transition when other magnetic anisotropies, such as the shape anisotropy for a ferromagnetic film, are taken into account. Our work suggests that the superconducting condensation energy in principle can trigger a reorientation of the magnetization of a thin-film ferromagnet upon lowering the temperature below $T_c$, in particular for ferromagnets with weak magnetic anisotropies.Comment: 11 pages, 10 figure

Tolosa-Hunt syndrome: a rare case report with uncommon imaging findings and discussion

A 45 year old diabetic but non hypertensive female presented with unilateral ptosis and complete external ophthalmoplegia on the left side. All the routine investigations were inconclusive. A signal void change was found in MRI study including angiogram of brain. On performing VEP (visually evoked potential), there was mild left optic pathway dysfunction (axonal and demyelinating). A probable diagnosis of Tolosa-Hunt Syndrome (THS) was made and the patient was started on steroids. She responded dramatically to the therapy and was discharged on steroids. Thus the diagnosis of THS was confirmed. On follow up after one month, both her ptosis and ophthalmoplegia had resolved completely. On subsequent follow up visits, she was free of any ophthalmological symptoms and signs

Statistical mechanics of asymmetric tethered membranes: spiral and crumpled phases

We develop the elastic theory for inversion-asymmetric tethered membranes and use it to identify and study their possible phases. Asymmetry in a tethered membrane causes spontaneous curvature, which in general depends upon the local in-plane dilation of the tethered network. This in turn leads to long-ranged interactions between the local mean and Gaussian curvatures, which is not present in symmetric tethered membranes. This interplay between asymmetry and Gaussian curvature leads to a new {\em double-spiral} phase not found in symmetric tethered membranes. At temperature $T=0$, tethered membranes of arbitrarily large size are always rolled up tightly into a conjoined pair of Archimedes' spirals. At finite $T$ this spiral structure swells up significantly into algebraic spirals characterized by universal exponents which we calculate. These spirals have long range orientational order, and are the asymmetric analogs of statistically flat symmetric tethered membranes. We also find that sufficiently strong asymmetry can trigger a structural instability leading to crumpling of these membranes as well. This provides a new route to crumpling for asymmetric tethered membranes. We calculate the maximum linear extent $L_c$ beyond which the membrane crumples, and calculate the universal dependence of $L_c$ on the membrane parameters. By tuning the asymmetry parameter, $L_c$ can be continuously varied, implying a {\em scale-dependent} crumpling. Our theory can be tested on controlled experiments on lipids with artificial deposits of spectrin filaments, in-vitro experiments on %\sout{artificial deposition of spectrin filaments on} red blood cell membrane extracts, %\sout{after %depletion of adenosine-tri-phosphate molecules} and on graphene coated on one side.Comment: 28 pages, 12 captioned figures. This is an accompanying longer version of our already submitted work, arXiv:1811.12440, containing all the technical details required for a thorough reading of arXiv:1811.1244

Rolled up or crumpled: phases of asymmetric tethered membranes

We show that inversion-asymmetric tethered membranes exhibit a new double-spiral phase with long range orientational order not present in symmetric membranes. We calculate the universal algebraic spiral shapes of these membranes in this phase. Asymmetry can trigger the crumpling of these membranes as well. In-vitro experiments on lipid, red blood cell membrane extracts, and on graphene coated on one side, could test these predictions.Comment: Significant modification on arXiv:1610.01992 and new results adde