Spontaneous emission spectrum in double quantum dot devices     

T Fujisawa  TH Oosterkamp  van der Wiel WG  BW Broer  R Aguado  S Tarucha  LP Kouwenhoven 《Science (New York, N.Y.)》1998,282(5390):932-935

A double quantum dot device is a tunable two-level system for electronic energy states. A dc electron current was used to directly measure the rates for elastic and inelastic transitions between the two levels. For inelastic transitions, energy is exchanged with bosonic degrees of freedom in the environment. The inelastic transition rates are well described by the Einstein coefficients, relating absorption with stimulated and spontaneous emission. The most effectively coupled bosons in the specific environment of the semiconductor device used here were acoustic phonons. The experiments demonstrate the importance of vacuum fluctuations in the environment for quantum dot devices and potential design constraints for their use for preparing long-lived quantum states.  相似文献   

Frictional melting during the rupture of the 1994 bolivian earthquake   总被引：1，自引：0，他引：1  

H Kanamori  DL Anderson  TH Heaton 《Science (New York, N.Y.)》1998,279(5352):839-842

The source parameters of the 1994 Bolivian earthquake (magnitude Mw = 8.3) suggest that the maximum seismic efficiency eta was 0.036 and the minimum frictional stress was 550 bars. Thus, the source process was dissipative, which is consistent with the observed slow rupture speed, only 20% of the local S-wave velocity. The amount of nonradiated energy produced during the Bolivian rupture was comparable to, or larger than, the thermal energy of the 1980 Mount St. Helens eruption and was sufficient to have melted a layer as thick as 31 centimeters. Once rupture was initiated, melting could occur, which reduces friction and promotes fault slip.  相似文献   

Association between burrow densities of two Australian freshwater crayfish (Engaeus sericatus and Geocharax gracilis: Parastacidae) and four riparian land uses     

Trevor S. March  Belinda J. Robson 《水产资源保护:海洋与淡水生态系统》2006,16(2):181-191

• 1. Freshwater crayfish that burrow into river banks are likely to be affected by riparian land uses that affect soil conditions and vegetation cover. The aim of this research was to determine whether burrow densities of two crayfish species (Engaeus sericatus Clark and Geocharax gracilis Clark) were associated with riparian land use and vegetation type in three streams in south‐west Victoria, Australia.
• 2. Four riparian land‐use categories were studied on each stream: native forest blocks; thin strips of mature native vegetation, fenced, with pasture adjacent; riparian pasture areas, fenced, with no cattle access to the stream; pasture and cattle access to the water's edge. Crayfish burrows were counted and a range of water quality and riparian condition variables were measured.
• 3. Native forest areas were found to have more than twice the densities of freshwater crayfish burrows than other land uses, which did not differ. Native forest areas also had higher mean burrow mound heights but lower burrow activity levels. Riparian characteristics also differed between land uses. In particular, soil compaction was the lowest in native forest areas, which also had better riparian condition scores and water quality than pasture areas.
• 4. This study suggests that cattle grazing may have reduced populations of burrowing crayfish in these streams, and that subsequent fencing and the presence of remnant native vegetation may be insufficient to ameliorate these effects. Blocks of native forest that remain on these streams may act as an important refuge for these species in agricultural areas.

Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

The electron beam attenuating properties of SuperFlab, Play-Doh, and wet gauze, compared to plastic water     

Nagata K  Lattimer JC  March JS 《Veterinary radiology & ultrasound》2012,53(1):96-100

Bolus material is used commonly with electron treatments. The purpose of this study was to compare the electron beam attenuating properties of SuperFlab, Play-Doh, and wet gauze to that of plastic water, and evaluate their characteristics as bolus materials for electron beam therapy. Electron beams of 5, 6, 7, 8, 10, and 12 MeV were used. Dose reduction from a range of bolus thicknesses from 2 mm to a thickness well beyond the thickness required to reach peak ioization was measured for each of the bolus materials to establish independent isodose curves. Measurements performed at the known water Dmax for all bolus materials indicated similar results for SuperFlab and plastic water with less than 3% difference for most energies. Play-Doh resulted in more attenuation or less dose buildup compared with plastic water, especially at lower energies. The difference was as high as 24.7% for the beam energy of 5 MeV for Play-Doh. Evaluation of the dose build up curves for all materials indicated the peak dose build up for wet gauze and Play-Doh occurred at lesser thicknesses compared to plastic water and SuperFlab, particularly at lower energies. If Play-Doh and wet gauze are to be used for electron bolus materials, dose build up curves should be established for the machine being used and the appropriate thickness of bolus material be chosen based on those curves.  相似文献   

Absence of REM rebound after barbiturate withdrawal   总被引：1，自引：0，他引：1  

I Feinberg  S Hibi  C Cavness  J March 《Science (New York, N.Y.)》1974,185(150):534-535

Administration of three different barbiturates reduced rapid eye movement (REM) sleep. Drug withdrawal led to a return to baseline REM] values without significant overshoot. Similar results are observed with administration of benzodiazepines in pharmacologically equivalent dosages; therefore, a distinction between these two drug classes on the basis of withdrawal effects on the sleep electroencephalogram appears unwarranted. Further investigation is required determine why high REM levels are sometimes associated with the withdrawal of sedative-hypnotic agents.  相似文献   

Excitation spectra of circular, few-electron quantum dots     

LP Kouwenhoven  TH Oosterkamp  MWS Danoesastro  M Eto  DG Austing  T Honda  S Tarucha 《Science (New York, N.Y.)》1997,278(5344):1788-1792

Studies of the ground and excited states in semiconductor quantum dots containing 1 to 12 electrons showed that the quantum numbers of the states in the excitation spectra can be identified and compared with exact calculations. A magnetic field induces transitions between the ground and excited states. These transitions were analyzed in terms of crossings between single-particle states, singlet-triplet transitions, spin polarization, and Hund's rule. These impurity-free quantum dots allow "atomic physics" experiments to be performed in magnetic field regimes not accessible for atoms.  相似文献   

Evaluation of effectiveness of Insegar (fenoxycarb 250 g/kg) WP against Phyllocnistis citrella Stainton (Lep., Gracillariidae) and its effect on Cales noacki How. (Hym., Aphelinidae)     

C. TH. Buchelos  M. Foudoulakis 《Anzeiger für Sch?dlingskunde》2000,43(3):19-21

Aiming to control the citrus leafminer Phyllocnistis citrella St. while at the same time protecting the biological equilibrium and mainly the beneficial insect Cales noacki, experiments have taken place in the regions of Argolis and Fthiotis, Greece in 1996 and 1997. Insegar (fenoxycarb) 2 5 WP was applied on young citrus trees. During 1996, the compound, applied every 10 days at a rate of 30 g/hI (with or without adjuvant), gave satisfactory protection from P. citrella without substantially harming C. noacki populations. No phytotoxicity symptoms were observed during the experiments.  相似文献   

Evaluation of effectiveness of Insegar (fenoxycarb 250 g/kg) WP against Phyllocnistis citrella Stainton (Lep., Gracillariidae) and its effect on Cales noacki How. (Hym., Aphelinidae)     

C. TH. Buchelos  M. Foudoulakis 《Anzeiger für Sch?dlingskunde》2000,73(1):19-21

Aiming to control the citrus leafminer Phyllocnistis citrella St. while at the same time protecting the biological equilibrium and mainly the beneficial insect Cales noacki, experiments have taken place in the regions of Argolis and Fthiotis, Greece in 1996 and 1997. Insegar (fenoxycarb) 2 5 WP was applied on young citrus trees. During 1996, the compound, applied every 10 days at a rate of 30 g/hI (with or without adjuvant), gave satisfactory protection from P. citrella without substantially harming C. noacki populations. No phytotoxicity symptoms were observed during the experiments.  相似文献   

Herbicide tank-mixing for post-emergence weed control in sugar beets     

C. N. GIANNOPOLITIS  TH. G. STROUTHOPOULOS 《Weed Research》1979,19(3):213-217

Tank-mixtures of selective herbicides were evaluated for 2 years on field-grown sugarbeets under two weed flora situations: (a) mixed floras of broad-leaved and grass weeds and (b) weed floras of broadleaves grown beyond their stages of greatest sensitivity to herbicides. In these situations single herbicides usually fail to provide satisfactory post-emergence weed control in sugarbeets. Of several tank-mixtures, which could be devised for use in the first situation, ethofurnesate + Betanal AM 11, diclofop-methyl + Betanal AM 11 and diclofop-methyl + metamitron gave synergistic phytotoxicity to sugarbeet seedlings. Synergism in weed control, becoming apparent by an accelerated appearance of the herbicidal effects, was obtained with the mixture alloxydimeton + Betanal AM 11. This mixture was not phytotoxic and appears to be the most efficient for simultaneous control of broad-leaved and grass weeds. From trials in the second situation it became apparent that the activity of metamitron, which was reduced on older weeds, could be restored by mixing with a non-phytotoxic oil or a low dose of Betanal AM 11. These mixtures should be useful when growth of sugarbeets has been retarded by carried-over herbicides, drought, frost, etc.  相似文献   

Evidence of genetic susceptibility to Hjarre's disease   总被引：2，自引：0，他引：2  

J Biely  B E March 《Avian diseases》1963,7(1):1-5

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