摘要:

A physicochemical model based on the modified classical heterogeneous nucleation theory was proposed to analyze the ice formation inside biological cells during freezing. According to this model, intracellular ice formation (IIF) may be catalyzed either by the plasma membrane via the effects of the external ice on the plasma membrane, calledsurface‐catalyzed nucleation(SCN), or by the intracellular particles, calledvolume‐catalyzed nucleation(VCN), depending on the freezing conditions. The model for IIF was coupled with the model describing the kinetics of water transport to predict the thermodynamic state of the cytoplasm.A method to estimate the nucleation frequency from the observed probability of nucleation was suggested. This method was based on the assumption that each cell has the same heteronucleating particles with identical properties to alter the nucleation kinetics in an identical way. This allowed the correlation of the experimental probability of IIF with the nucleation rate. It was suggested that the uncertainties in the experimental conditions could be minimized if cells were cooled at rapid rates to prevent water transport during freezing. The model was applied to mouse oocytes at metaphase II. Correlation of the theory with the experimental kinetics of the cumulative fraction of IIF revealed preexponentional factors of 3.56×108(m2 s)−1and 1.84×1050(m3 s)−1, and exponential factors of 4.6×109and 1.08×1012K5for SCN and VCN, respectively. The contact angle between the internal surface of the plasma membrane and the ice cluster for SCN, &thgr;, was determined to be 35° for freezing in isotonic solutions (285 mosm) increasing linearly to 47° in hypertonic solutions (1035 mosm). SCN was active between ∼−5 and −20 °C in the presence of external ice. It is suggested that the presence of external ice alters the plasma membrane through its chemical, electrical, mechanical, ionic, and thermal effects, to make it an energetically favorable site for heterogeneous nucleation. For VCN, lower and upper limits for &thgr; andRwere found to be 60°<&thgr;<100° and 10−7<R<4×10−7cm, respectively. VCN was active between ∼−30 and −35 °C.

ISSN:0021-8979    

DOI:10.1063/1.345670

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We present experimental results of field‐enhanced photorefractive two‐beam coupling and gain in Cr‐doped strontium barium niobate crystals and its dependence on dopant concentrations. Increases in the exponential gain factor by more than a factor of 2 were observed by applying a field of up to 10 kV/cm. This property has potential applications such as switchable optical phase conjugators, limiters, and thresholding devices.

ISSN:0021-8979    

DOI:10.1063/1.345671

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A hydrogenated amorphous silicon (a‐Si:H)p‐i‐nsolar cell with a two‐layer back electrode is proposed. The new type of back electrode consists of a conventional Al layer and an amorphous silicide layer. The properties of amorphous Cr‐silicide film and thermal stability ofa‐Si:Hp‐i‐nsolar cells with a two‐layer back electrode are studied. The experimental results show that an amorphous Cr‐silicide layer can prevent the thermal diffusion of Al from going intoa‐Si:H, and thus can improve the thermal stability of thea‐Si:H solar cell.

ISSN:0021-8979    

DOI:10.1063/1.345643

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Atomic indium, produced by the pyrolysis of trimethylindium (TMIn) during metalorganic chemical vapor deposition, has been directly observed using resonant fluorescence spectroscopy. The indium fluorescence signal is linear with TMIn flow rate at a susceptor temperature of 500 °C above a small background threshold level. The threshold for the observation of an indium signal is 325 °C. Addition of trimethylantimony (TMSb) at concentrations less than those required for normal InSb epitaxial growth results in quenching of the indium signal.

ISSN:0021-8979    

DOI:10.1063/1.345644

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In order to gain an insight into the effects of a space environment on materials, thin aluminum samples were exposed to an oxygen plasma produced by an electron beam. Using Rutherford backscattering spectrometry the samples exposed to the oxygen plasma were compared to samples exposed to ordinary oxygen gas. The comparison revealed a considerable increase in oxygen diffusion in the samples exposed to the charged particle environment. The amount of oxygen diffusion depends on the duration of the plasma exposure.

ISSN:0021-8979    

DOI:10.1063/1.345645

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In order to increase the laser energy through energy conversion of the pumping light, the converter dye BBQ was mixed in the laser dye LD490 solutions. The laser was pumped by an Ar flashlamp with a relatively long pulse width. Various concentrations of dye mixture LD490+BBQ in methanol were used. The experimental results show that the laser output energy increases by 180% with a dye mixture made of 4.5×10−6mol/l  BBQ over the maximum output obtainable with the laser dye alone, while the laser power increases by 92% with the same conditions. Comparison with previous work [K. S. Hanetal., J. Appl. Phys.60, 3414 (1986)] is discussed.

ISSN:0021-8979    

DOI:10.1063/1.345646

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The minimum fluence at which a laser pulse (FWHM 20 ns; 248 nm) causes a change in the surface of a film of polyethylene terephthalate (=PET) or polyimide (KaptonTM) in air has been measured by probing the surfaces with visible laser pulses of <1 ns at delay times of 10–10 000 ns. At fluences at which a single pulse left a permanent etch pit, the probe pulse showed an intense and rapid (<60 ns) darkening of the surface which may be attributed to the scattering of the beam by gas bubbles at the polymer surface. In 100 ns, a blast wave was visible which could be tracked for over 1000 ns. At the end (∞ ns), the polymer surface was not darkened but an etch pit was apparent. Progressively decreasing the fluence showed that even at fluences <0.025 J/cm2for PET and<0.050 J/cm2for Kapton, a single pulse transiently blackened the surface but did not leave an etch pit. The threshold for the ablative photodecomposition of these polymers appears to lie at a value of the fluence that is well below the threshold for measurable etching by a single laser pulse.

ISSN:0021-8979    

DOI:10.1063/1.345647

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

It is shown that for currently attainable experimental parameters, classical electrodynamics is perfectly adequate for the prediction of all features of harmonic generation in intense laser‐free electron scattering. While the customary semiclassical approach is characterized by lengthy calculations and unwieldy expressions, the classical framework arrives at the same results in only a few lines, is valid for arbitrary electron injection energies, and provides at the same time an intuitive understanding of the predicted features. This is confirmed by graphical comparisons of the various available cross sections, which also show some of the published results to be incorrect.

ISSN:0021-8979    

DOI:10.1063/1.345648

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

High crystalline quality GaAs/Ge/GaAs heterostructures have been grown on both straight and slightly misoriented GaAs(100) substrates by molecular beam epitaxy. High‐energy electron diffraction was used to study the sublattice rotation of GaAs on epitaxial Ge dependent on the use of a Ga or As prelayer. On straight (100) substrates, a Ga prelayer was observed to rotate the GaAs surface reconstruction by &pgr;/2 while an As prelayer preserved the GaAs orientation observed prior to Ge deposition. No rotation of the surface was observed on substrates tilted 4° towards [011]. We present a growth model to explain these results.

ISSN:0021-8979    

DOI:10.1063/1.345649

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We present the growth and optical properties of Pb1−xEuxTe films (0<x<0.55) prepared by a co‐evaporation technique onto BaF2(111) substrates. They crystallize in a NaCl‐type structure. The lattice parameter increases asxincreases but not in accordance with Vegard’s law. The optical band gap increases with increasingxvalues. Our data seem to indicate the stability of Eu2+for 0<x<0.55.

ISSN:0021-8979    

DOI:10.1063/1.345625

出版商:AIP    

年代:1990

数据来源: AIP