11,333 research outputs found
Thermotunnel refrigerator with vacuum/insulator tunnel barrier: A theoretical analysis
The authors use two insulator layers in thermotunnel refrigerator to modify
the shape of the tunneling barrier so that electrons with high kinetic energy
pass it with increased probability. Theoretical analysis show that the overall
tunneling current between the electrodes contains an increased number of high
kinetic energy electrons and a reduced number of low energy ones, leading to
high efficiency. The particular case of vacuum gap and solid insulator layer is
calculated using digital methods. Efficiency remains high in the wide range of
the emitter electric field. The cooling coefficient is found to be as high as
40%-50% in the wide range of the emitter electric field.Comment: 9 pages, 3 figure
Monte Carlo simulations of random copolymers at a selective interface
We investigate numerically using the bond--fluctuation model the adsorption
of a random AB--copolymer at the interface between two solvents. From our
results we infer several scaling relations: the radius of gyration of the
copolymer in the direction perpendicular to the interface () scales
with , the interfacial selectivity strength, as
where is the usual Flory exponent and
is the copolymer's length; furthermore the monomer density at the interface
scales as for small . We also determine numerically the
monomer densities in the two solvents and discuss their dependence on the
distance from the interface.Comment: Latex text file appended with figures.tar.g
Pregnancy-associated breast cancer - Special features in diagnosis and treatment
For obvious psychological reasons it is difficult to associate pregnancy - a life-giving period of our existence with life-threatening malignancies. Symptoms pointing to malignancy are often ignored by both patients and physicians, and this, together with the greater difficulty of diagnostic imaging, probably results in the proven delay in the detection of breast cancers during pregnancy. The diagnosis and treatment of breast cancer are becoming more and more important, as the fulfillment of the desire to have children is increasingly postponed until a later age associated with a higher risk of carcinoma, and improved cure rates of solid tumors no longer exclude subsequent pregnancies. The following article summarizes the special features of the diagnosis and primary therapy of pregnancy-associated breast cancer with particular consideration of cytostatic therapy
Towards a precision computation of f_Bs in quenched QCD
We present a computation of the decay constant f_Bs in quenched QCD. Our
strategy is to combine new precise data from the static approximation with an
interpolation of the decay constant around the charm quark mass region. This
computation is the first step in demonstrating the feasability of a strategy
for f_B in full QCD. The continuum limits in the static theory and at finite
mass are taken separately and will be further improved.Comment: Lattice2003(heavy), 3 pages, 2 figure
High efficiency thermionic converter studies
The objective is to improve thermionic converter performance by means of reduced interelectrode losses, greater emitter capabilities, and lower collector work functions until the converter performance level is suitable for out-of-core space reactors and radioisotope generators. Electrode screening experiments have identified several promising collector materials. Back emission work function measurements of a ZnO collector in a thermionic diode have given values less than 1.3 eV. Diode tests were conducted over the range of temperatures of interest for space power applications. Enhanced mode converter experiments have included triodes operated in both the surface ionization and plasmatron modes. Pulsed triodes were studied as a function of pulse length, pulse potential, inert gas fill pressure, cesium pressure, spacing, emitter temperature and collector temperature. Current amplifications (i.e., mean output current/mean grid current) of several hundred were observed up to output current densities of one amp/sq cm. These data correspond to an equivalent arc drop less than 0.1 eV
Weekly Paclitaxel plus Capecitabine versus Docetaxel Every 3 Weeks plus Capecitabine in Metastatic Breast Cancer
Background. We performed a randomized phase II study comparing efficacy and toxicity of weekly paclitaxel 80 mg/m2 (Weetax) with three weekly docetaxel 75 mg/m2 (Threetax), both in combination with oral capecitabine 1000 mg/m2 twice daily for 2 weeks followed by a 1-week break.
Patients. Thirty-seven women with confirmed metastatic breast cancer were randomized.
Results. Median TTF was 174 (Weetax) versus 147 days (Threetax) (=0.472). Median OS was 933 (Weetax) versus 464 days (Threetax) (=0.191). Reasons for TTF were PD 8/18 (Weetax), 9/19 (Threetax); and toxicity: 8/18 (Weetax), 8/19 (Threetax). ORR was 72% (Weetax) versus 26% (Threetax) (=0.01). The Threetax-combination resulted in a higher incidence of leuco-/neutropenia compared to Weetax. Grade II anemia was more pronounced in the Weetax group. No difference was found in quality of life.
Conclusion. Taxanes in combination with capecitabine resulted in a high level of toxicity. Taxanes and capecitabine should be considered given sequentially and not in combination
Determining the efficiency of residential electricity consumption
Increasing energy efficiency is a key global policy goal for climate protection.
An important step towards an optimal reduction of energy consumption is the identification
of energy saving potentials in different sectors and the best strategies for increasing
efficiency. This paper analyzes these potentials in the household sector by estimating the
degree of inefficiency in the use of electricity and its determinants. Using stochastic frontier
analysis and disaggregated household data, we estimate an input requirement function
and inefficiency on a sample of 2,000 German households. Our results suggest that the
mean inefficiency amounts to around 20%, indicating a notable potential for energy savings.
Moreover, we find that the household size and income are among the main determinants
of individual inefficiency. This information can be used to increase the cost-efficiency of
programs aimed to enhance energy efficiency
Selective Formation of a Trisubstituted Alkene Motif by trans-Hydrostannation/Stille Coupling: Application to the Total Synthesis and Late-Stage Modification of 5,6-Dihydrocineromycin B
Countless natural products of polyketide origin have an E-configured 2-methyl-but-2-en-1-ol substructure. An unconventional entry into this important motif was developed as part of a concise total synthesis of 5,6-dihydrocineromycin B. The choice of this particular target was inspired by a recent study, which suggested that the cineromycin family of antibiotics might have overlooked lead qualities, although our biodata do not necessarily support this view. The new approach consists of a sequence of alkyne metathesis followed by a hydroxy-directed trans-hydrostannation and a largely unprecedented methyl-Stille coupling. The excellent yield and remarkable selectivity with which the signature trisubstituted alkene site of the target was procured is noteworthy considering the rather poor outcome of a classical ring-closing metathesis reaction. Moreover, the unorthodox ruthenium-catalyzed trans-hydrostannation is shown to be a versatile handle for diversity-oriented synthesis
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