Radiation damage in stained catalase at low temperature.

Radiation damage, which occurs in the beam of the electron microscope, has been studied in uranyl acetate stained crystals. Damage is observed in terms of the disappearance of higher orders of the electron diffraction pattern. In this study it has been found that the damage at very low specimen temperatures proceeds both more rapidly and to a greater final degree than is the case at room temperature.     

Radiation damage to microdroplets at low temperature

The effect of low temperatures on the stability of characteristic signals during electron probe analysis of microdroplets was investigated. The kinetics of the characteristic Na, K and Cl signals from lyophilized droplets of either KCl or NaCl salts were observed for 1200 s in an electron microprobe whose specimen stage temperature was either 133 K or room temperature. Samples were irradiated with 15 keV electrons, at beam current densities ranging from 7 to 70 A m^?2. Initial count rates were lower for the same samples at 133 K than at room temperature. At 133 K all the signals measured increased at the start and then, in some cases, decreased. Increases were more pronounced for measurements made at the lowest beam current density (i.e. the lowest electron dose), and for samples with the highest mass thickness; they were also more marked for KCl than for NaCl samples. At 133 K, measurements after 10 s irradiation showed no proportionality between X-ray intensity and the concentration of the elements, and proportionality was only restored when droplets had been irradiated for some time and count rates became nearer to the values measured at room temperature. Whether or not these observations reveal the existence of a fundamental physical process or a technical failure is still unknown. In no case was characteristic signal stability improved by the use of a cold stage.     

Radiation damage relative to transmission electron microscopy of biological specimens at low temperature: a review.

When biological specimens are irradiated by the electron beam in the electron microscope, the specimen structure is damaged as a result of molecular excitation, ionization, and subsequent chemical reactions. The radiation damage that occurs in the normal process of electron microscopy is known to present severe limitations for imaging high resolution detail in biological specimens. The question of radiation damage at low temperatures has therefore been investigated with the view in mind of reducing somewhat the rate at which damage occurs. The radiation damage protection found for small molecule (anhydrous) organic compounds is generally rather limited or even non-existent. However, large molecular, hydrated materials show as much as a 10-fold reduction at low temperature in the rate at which radiation damage occurs, relative to the damage rate at room temperature. In the case of hydrated specimens, therefore, low temperature electron microscopy offers an important advantage as part of the overall effort required in obtaining high resolution images of complex biological structures.     

Radiation damage in electron microscopy of organic materials: effect of low temperatures.

As measured by the life-time of their electron diffraction patterns, the radiation sensitivity of anthracene and coronene at 500 kV is reduced by a factor of three to four at liquid helium temperature in comparison to room temperature, For l-valine the ratio is about 1-8 but there is a wide variation in the results, possibly due to differences in crystal thickness. The end-dose at 20 degrees K for valine is equivalent to 13 electrons/A2; for anthracene and coronene it is about 600 electrons/A2 at room temperature. The variation of end-dose with temperature shows that at least two mechanisms must be involved in damage to such compounds, possibly concerning the breaking of intermolecular and intramolecular bonds, respectively.     

Rotating sample holder at low temperature

A low temperature rotary device (cryoturbine) for use in extended x-ray-absorption fine structure measurements in fluorescence mode has been designed and manufactured. The instrument works at a temperature close to liquid Nitrogen and can reach frequencies up to 100 Hz with good stability. The rotation speed is measured with a light-emitting diode driven in stroboscopic mode by a simple electronic circuit.     

防锈铝合金5083锻件的焊接方法

介绍了防锈铝合金5083的力学性能,分析了其在低温阀门上尤其是在空气分离设备上应用的特点。论述了铝合金阀门的焊接工艺方法。     

Sensitive temperature gradiometer for use at low temperatures

A device capable of very sensitive temperature gradient measurements in the presence of relatively large ambient temperature fluctuations is described. The device uses a pair of 'matched' superconducting thin films in a bridge arrangement, with a SQUID magnetometer probe as the null detector.     

低温状态下的材料法向发射率测量

研究了在-60~50℃条件下准确测量材料法向发射率的方法。基于发射率定义建立了材料法向发射率测量模型。为屏蔽环境杂散辐射与大气吸收的影响,利用真空液氮背景通道搭建了低温状态下材料发射率测量装置。测量了氧化铜与高发射率陶瓷两种样品的法向发射率随温度、波长的变化情况。结果表明:两种样品的法向光谱发射率均随波长增加而降低;随温度的升高,氧化铜样品法向积分发射率稳定为0.850±0.012,陶瓷样品的法向积分发射率降低了0.124。最后,实现了低温状态下红外光谱辐射的高精度采集,对低温状态下材料法向光谱发射率测量结果的不确定度进行了评定,得到的结果显示其相对扩展不确定度小于6.0%。     

Patterned anvils for high pressure measurements at low temperature

Multiprobe high pressure measurements require electrical leads in the sample chamber. Compared to conventional wire-based techniques, metallic tracks patterned onto the anvil surface improve reliability and ease of use, and enable novel and more demanding measurements under high pressure. We have developed new anvil designs based on sputter-deposited tracks on alumina and moissanite anvils. These anvils allow convenient and reliable measurements of electrical transport properties or of the magnetic susceptibility under hydrostatic conditions, as demonstrated by test measurements on Pb and Ca(3)Ru(2)O(7).     

Radiation damage in silicon detectors

A review is presented of the effects of radiation damage on silicon detectors, which are being considered for high energy physics applications. The main degradation in performance is an increase in leakage current, which can be well characterized by an empirical damage constant for many radiations. A summary of data on damage constants is given. A brief discussion of annealing effects in terms of band gap level changes is included.     

The reliability of soldered joints produced at a low temperature

Under severe service conditions of electronic instruments (at elevated temperatures and vibrations in electronic systems), failures in their operation frequently occur. Severe intrinsic thermal conditions of operating instruments may cause such failures. However, malfunctions in electronic devices may often be due to defects in soldered joints that were made at lowered temperatures. An approach is proposed that makes it possible to considerably improve the reliability of soldered joints.     

Note: ferrule-top atomic force microscope. II. Imaging in tapping mode and at low temperature

In a recent paper [D.Chavan et al., Rev. Sci. Instrum. 81, 123702 (2010)] we have demonstrated that ferrule-top cantilevers, obtained by carving the end of a ferruled fiber, can be used for contact mode atomic force microscopy in ambient conditions. Here we show that those probes can provide tapping mode images at both room and cryogenic temperatures (12 K).     

Glucose alone does not completely hydrate bacteriorhodopsin in glucose-embedded purple membrane

Glucose embedding is a simple and highly effective method for preparing biological macromolecules for high-resolution electron microscopy. The investigation of conditions that can trap the M-state intermediate in the bacteriorhodopsin (bR) photocycle has revealed, however, that when glucose-embedded bR is prepared at ambient humidity, it does not fully retain the capability to execute a proper photocycle. However, ‘native’ photocycle properties are returned after glucose-embedded samples are equilibrated at 81% relative humidity. Equilibration at relative humidities significantly higher than 81% causes glucose to dissolve in its own water of hydration, resulting in samples that may be too thick to be suitable for electron microscopy. The results obtained with bR indicate that caution should be taken with other biological specimens, and it cannot be assumed that glucose-embedded biological macromolecules retain completely their native, hydrated structure, even when high-resolution electron diffraction patterns are obtained. Equilibration of such samples at high humidity may generally be a worthwhile precaution when using the glucose-embedding technique.     

Combined quick freezing,freeze-drying,and embedding tissue at low temperature and in low viscosity resins

The techniques of quick freezing and freeze-drying provide an alternative to the more classical methodologies of chemical fixation and dehydration with organic solvents. It is possible to embed freeze-dried tissue in low viscosity resins, either at room temperature or at subzero temperatures in Spurr's resin or Lowicryl K4M, respectively. The choice of embedding medium affords additional flexibility in postdrying and embedding conditions, since Spurr's resin allows vapor fixation with osmium tetroxide and thermal polymerization. Osmium tetroxide is not recommended for Lowicryl resins, but these media permit polymerization at subzero temperatures with ultraviolet light. Both resins have unique advantages that may be utilized, depending upon the purpose of the embedding. In this paper, we discuss the details of preparing smooth muscle, from rabbit renal artery, by quick freezing and freeze-drying, as well as methods for the embedding of the freeze-dried tissue in both Spurr's resin and Lowicryl K4M. Although we have previously reported the ultrastructure of smooth muscle embedded in Spurr's low viscosity resin, the combination of freeze-drying and infiltration in Lowicryl K4M represents a new approach that allows the elimination of chemical fixation, dehydration with organic solvents, and heat polymerization of the embedding medium.     

Preparation of aqueous standards for low temperature X-ray microanalysis.

A technique, using Nuclepore polycarbonate membrane filters as a containing medium for very small volumes of ionic standard solutions, to produce homogeneous ice standards is described. The standards are suitable for use in a scanning electron microscope. The relationship between elemental X-ray counts and ionic concentration is found to be linear. The method is rapid and simple. Minimum detectable concentrations are given.