Intensification of heat exchange with surface boiling of water in pipes with annular turbulizer

The article demonstrates the possibility of greatly intensifying heat exchange with surface boiling of water moving in pipes with annular diaphragm.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 4, pp. 569–574, October, 1984.     

Influence of a low-frequency acoustic field on the carillary impregnation of gas-saturated porous systems

Experimental results on the influence of a low-frequency acoustic field on the capillary impregnation of gas-saturated artificially cemented and noncemented porous rock samples are given. It is found that the impregnation rate can be increased and gas can be displaced completely from the porous collector on account of the field action.Institute of Oil and Gas Problems, Moscow. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 63, No. 2, pp. 232–236, August, 1992.     

Using a multijunction microfluidic device to inject substrate into an array of preformed plugs without cross-contamination: comparing theory and experiments

In this paper we describe a multijunction microfluidic device for the injection of a substrate into an array of preformed plugs carried by an immiscible fluid in a microchannel. The device uses multiple junctions to inject substrate into preformed plugs without synchronization of the flow of substrate and the array of preformed plugs of reagent, which reduces cross-contamination of the plugs, eliminates formation of small droplets of substrate, and allows a greater range of injection ratios compared to that of a single T-junction. The device was based on a previously developed physical model for transport that was here adapted to describe injection and experimentally verified. After characterization, the device was applied to two biochemical assays, including evaluation of the enzymatic activity of thrombin and determination of the coagulation time of human blood plasma, which both provided reliable results. The reduction of cross-contamination and greater range of injection ratios achieved by this device may improve the processes that involve addition and titration of reagents into plugs, such as high-throughput screening of protein crystallization conditions.     

Peculiarities of the total energy distribution of field emission electrons from graphene-like structures

It is demonstrated that the field emission from graphene-like structures (GLSs) has a very low excitation threshold (about two orders of magnitude lower than that of metals and semiconductors). It is shown that the total energy distribution (TED) of field emission electrons from GLSs differs considerably from the spectra obtained for metals. The existence of two maxima of this distribution (spaced 0.7–1.7 eV apart), significant broadening of the energy distribution, and a shift of these maxima depending on the electric field intensity are reported. The resonance nature of low-threshold field emission from GLSs is confirmed.     

Intensification of heat transfer during vapor condensation on the outside surface of vertical tubes with annular swirl vanes

It is shown that it is possible to significantly intensity heat exchange in vertical condensers consisting of tubes with annular membranes inside and grooves on the outside.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 2, pp. 184–189, August, 1984.     

A constraint sampling approach for multi-stage robust optimization

We propose a tractable approximation scheme for convex (not necessarily linear) multi-stage robust optimization problems. We approximate the adaptive decisions by finite linear combinations of prescribed basis functions and demonstrate how one can optimize over these decision rules at low computational cost through constraint randomization. We obtain a-priori probabilistic guarantees on the feasibility properties of the optimal decision rule by applying existing constraint sampling techniques to the semi-infinite problem arising from the decision rule approximation. We demonstrate that for a suitable choice of basis functions, the approximation converges as the size of the basis and the number of sampled constraints tend to infinity. The approach yields an algorithm parameterized in the basis size, the probability of constraint violation and the confidence that this probability will not be exceeded. These three parameters serve to tune the trade-off between optimality and feasibility of the decision rules and the computational cost of the algorithm. We assess the convergence and scalability properties of our approach in the context of two inventory management problems.     

Robust hedging strategies

While investing in foreign assets may bring additional benefits in terms of risk diversification, it may also expose the portfolio to a further source of risk derived from changes in the value of the foreign currencies. Hedging strategies for international portfolios have usually focused on the use of forward contracts to mitigate the currency risk. We propose an alternative formulation aimed at the reduction of the overall portfolio risk by assuming the returns are uncertain and maximizing the portfolio return for the worst possible outcome of the returns. This technique known as robust optimization provides a first guarantee on the portfolio value thanks to the non-inferiority property. We further complement our approach with forward contracts on the foreign exchange rates and options on the assets. Because the total return on any asset will be the product of its local return and currency return, the models proposed are bilinear and non convex. A reformulation of both the uncertainty set and the objective function as a semidefinite problem will yield an approximate tractable model. We compare the hedging alternatives proposed with simulated and historical market data and conclude on their relative benefits.