LET calibration for CR-39 detectors in different oxygen environments

High LET (linear energy transfer) radiation is the main contributor to the radiation field in low Earth orbit (LEO) in terms of dose equivalent. CR-39 plastic nuclear track detectors (PNTDs) can measure the LET spectrum and charge spectrum for the complicated radiation field in space. Previous research indicated that the sensitivity of CR-39 is different for CR-39 PNTDs working in different oxygen environments. LET calibration for CR-39 detectors in different oxygen environments is needed. Almost all the previous LET calibration work was carried out for CR-39 detectors in good-oxygen condition, LET calibration work for CR-39 in poor-oxygen condition has not been conducted until our work. Systematic LET calibrations were carried out by JSC-SRAG (Space Radiation Analysis Group) for CR-39 detectors working in different oxygen environments and abundant results of LET calibrations were obtained. This paper introduces the method for CR-39 LET calibration, presents and discusses the calibration results and some applications.     

Conversion between anticipating and lag chaos synchronization induced by different bias current levels in mutually delay-coupled semiconductor lasers

Based on a mutually delay-coupled semiconductor lasers (SLs) system, through adjusting the bias current of a SL and fixing that of the other one, the conversion between anticipating and lag chaos synchronization of this system has been experimentally observed for the first time. Experimental results show that for two SLs with the similar operation parameters, the SL biased at a relatively higher current level plays a leader role due to its relatively higher output power. Considering that the SL with a higher bias current level will oscillate at a longer wavelength, the SL with a longer wavelength becomes the leader, which provides a synchronization conversion scheme via by purely electronic current drive. Furthermore, the corresponding theoretical analyses have been given, and show that whether the SL with a longer or shorter wavelength becomes the leader mainly depends on the approach of the driving of frequency detuning between the two SLs.     

Liquid ionization chambers for LET determination

Modern radiotherapy facilities for cancer treatment such as the Heavy Ion Therapy Centre (HIT) in Heidelberg (Germany) enable sub millimetre precision in dose deposition. For the measurement of such dose distributions and characterization of the particle beams, detectors with high spatial resolution and high sensitivity are necessary. For exact dosimetry which is done using ionization chambers (ICs), the recombination taking place in the IC has to be known. Up to now, recombination is corrected phenomenologically and more practical approaches are currently used. Nevertheless, Jaffés theory of columnar recombination was designed to model the detector efficiency of an ionization chamber. Here, we have shown that despite the approximations and simplification made, the theory is correct for the LETs typically found in clinical radiotherapy employing particles from protons to carbon ions. As no exact closed solution is available, a numerical solver was programmed.     

Conversion issues between microwave radiance and brightness temperature

Microwave radiances are usually converted into brightness temperatures for data assimilation and retrievals. The Rayleigh-Jeans approximation has been believed to be a good approximation for the conversion at low frequencies, but inaccurate at high frequencies. However, the simplified radiative transfer models under the Rayleigh-Jeans approximation (hereafter referred as BT-RTE) have been successfully applied in radiance simulations for frequencies below 183 GHz, which has somewhat puzzled the radiative transfer community. This paper clarifies the confusion. In addition, the conversion formula for the third and the fourth Stokes components are derived.Simulations for a polarized sensor, the Special Sensor Microwave Imager and Sounder, show that the BT-RTE is generally accurate. Results for a polarimetric sensor, WINDSAT, show that the third and the fourth Stokes radiances should be converted using the exact conversion formula given in this study rather than using a direct Planck function conversion.     

让世界跳跃的人--马克思*普朗克

回顾了普朗克在物理学上的贡献和对爱因斯坦的帮助，挖掘了他的物理思想，得到对他公正的认识．     

Relative stability of cubic and different hexagonal forms of boron nitride

Boron nitride in the cubic form has a hardness approaching that of diamond. It is synthesized from a hexagonal graphitic phase. The physical behavior of the hexagonal phase depends upon the nature of layer stacking. This stacking is investigated using density functional approaches with the local density approach being far more successful than the generalized gradient approach. Various forms of the AaAa… stacking are predicted to be stable suggesting the existence of slightly different phases of the material. At the same time the energy differences between the stacking geometries is small and associated with small changes in the inter-layer spacing. This could have implications for the h-BN to c-BN transformation.     

Comparison of different forms of compression using wearable digital hearing aids

Four different compression algorithms were implemented in wearable digital hearing aids: (1) The slow-acting dual-front-end automatic gain control (AGC) system [B. C. J. Moore, B. R. Glasberg, and M. A. Stone, Br. J. Audiol. 25, 171-182 (1991)], combined with appropriate frequency response equalization, with a compression threshold of 63 dB sound pressure level (SPL) and with a compression ratio of 30 (DUAL-HI); (2) The dual-front-end AGC system combined with appropriate frequency response equalization, with a compression threshold of 55 dB SPL and with a compression ratio of 3 (DUAL-LO). This was intended to give some impression of the levels of sounds in the environment; (3) Fast-acting full dynamic range compression in four channels (FULL-4). The compression was designed to minimize envelope distortion due to overshoots and undershoots; (4) A combination of (2) and (3) above, where each applied less compression than when used alone (DUAL-4). Initial fitting was partly based on the concept of giving a flat specific-loudness pattern for a 65-dB SPL speech-shaped noise input, and this was followed by fine tuning using an adaptive procedure with speech stimuli. Eight subjects with moderate to severe cochlear hearing loss were tested in a counter-balanced design. Subjects had at least 2 weeks experience with each system in everyday life before evaluation using the Abbreviated Profile of Hearing Aid Benefit (APHAB) test and measures of speech intelligibility in quiet (AB word lists at 50 and 80 dB SPL) and noise (adoptive sentence lists in speech-shaped noise, or that same noise amplitude modulated with the envelope of speech from a single talker). The APHAB scores did not indicate clear differences between the four systems. Scores for the AB words in quiet were high for all four systems at both 50 and 80 dB SPL. The speech-to-noise ratios required for 50% intelligibility were low (indicating good performance) and similar for all the systems, but there was a slight trend for better performance in modulated noise with the DUAL-4 system than with the other systems. A subsequent trial where three subjects directly compared each of the four systems in their everyday lives indicated a slight preference for the DUAL-LO system. Overall, the results suggest that it is not necessary to compress fast modulations of the input signal.     

Calculation of LET in SEE simulation by pulsed laser

A key point in SEE (Single Event Effect) simulation experiment is how to calculate the equivalent LET (Linear Energy Transfer) for laser pulse. In this paper, the calculation method considering the influences of nonlinear absorption in semiconductor, reflection and refraction on device surface and other factors is presented. Simultaneously an instance of calculation is provided, with the result in good agreement with the SEU (Single Event Upset) threshold measured by heavy ions.     

Three-dimensional difference extraction between two similar object forms

A technique using direct object coding is described which permits the extraction of object form differences between two suitably illuminated objects in a three-dimensional manner. While contour differences are visualized similarly as by the usual film coding methods, the form deviations in the direction normal to the film plane lead to Moiré fringes. The structured illumination is achievable coherently or incoherently.     

Secondary particle contribution to LET spectra on LDEF

Four experiments utilizing passive detectors (P0006, P0004, A0015, M0004) were flown on LDEF to study the radiation environment. These experiments have been summarized in a companion paper (Benton et al., 1996). One of the experimental goals was to measure LET spectra at different locations and shielding depths with plastic nuclear track detectors (PNTD). It was found that the LET spectra extended well above the LET cutoff imposed by the geomagnetic field on GCR particle penetration into LEO. The high LET particles detected were mostly short-range (range < 2000 μm), indicating that they were secondaries produced locally within the PNTD. The presence of these high LET particle fluences is important for the determination of dose equivalent because of the high Quality Factors (Q) involved. A relatively small fraction of particle fluence can contribute a large fraction of dose equivalent.

Short-range, inelastic secondary particles produced by trapped protons in the South Atlantic Anomaly (SAA) were found to be a major contributor to the LET spectra above 100 keV/μm. The LET spectra were found to extend beyond the 137 keV/μm relativistic GCR Fe peak to over 1000 keV/μm. The high LET tail of the LET spectra was measured in CR-39 and polycarbonate PNTDs using different techniques. GCR made a relatively modest contribution to the LET spectra as compared to the contributions from short-range secondary particles and stopping protons.

LET spectra intercomparisons were made between LDEF measurements and exposures to 154 MeV accelerated proton beams. The similarities support the role of nuclear interactions by trapped protons as the major source of secondary particles in the PNTDs. Also techniques were employed to reduce the range cutoff for detection of the short-range secondaries to 1 μm, so that essentially all secondary particles were included in the LET spectra. This has allowed a more realistic assessment of secondary contribution to dose equivalent.

Comparisons of measured and calculated LET spectra have been made that demonstrate the need for more accurate modeling of secondary particles in radiation transport codes. Comparisons include preliminary calculations in which attempts have been made to include secondary particles.     

让新实验诉说量子理论

在1998年完成和分析的几个新的物理实验显示了量子理论的微妙性,包括“波粒二重性”以及二粒子缠结态的不可分性.本文的分析表明:测量在破坏原来存在于客体及其环境间的量子相干性时必然要改变客体.因而“物理实在”应在两个层次上定义:“自在之物”与“为我之物”.量子力学中的波函数则正起了通过“虚拟的测量”将这两个层次的物质联系起来的作用.     

The effect of different treatments on fractal forms of gallium arsenide surface

The surface of epitaxial gallium arsenide (as-grown and subjected to standard chemical treatments for producing metal-GaAs electrical contacts) has been studied by atomic force microscopy. It was shown that the surface relief can be characterized by fractal relief in the local approximation. As-grown epitaxial n-GaAs layers have lower values of the mean relief irregularity and roughness and reveal high surface homogeneity. The most marked relief changes are observed due to plasmachemical deposition of silicon dioxide and its removal in a buffered etch and deionized water rinse. The following finishing treatments make the surface more smooth and homogeneous, especially in ammonia-water mixture, which gives almost an ideal (Gaussian) distribution of irregularities and phase contrast in most cases. The fractal dimensionality of the studied surfaces changes in the relatively narrow limits D _f = 2.5−2.8. The values of the local approximation limit L determining the boundary of the applicability of the fractal approach when describing the surfaces change from 0.039 to 10.99 μm depending on the kind of treatment.     

Role of NMDA receptor subtypes in different forms of NMDA-dependent synaptic plasticity

Background  

The involvement of different NMDA receptor (NMDAR) subunits has been implicated in several forms of synaptic plasticity. However, it is still controversial to what extent the involvement is specific, and little is known about the role of NMDAR subunits in certain "non-conventional" forms of plasticity. In this study we used subunit-specific blockers to test the roles of NR2A- and NR2B-containing NMDARs in a type of chemical long-term depression (LTD) induced by brief bath application of the NMDAR agonist NMDA to hippocampal slices from 12–18 days old rats. For comparison, we also examined other forms of plasticity, including a "slow LTD" induced by 0.1 Hz stimulation under low Mg²⁺ conditions as well as long-term potentiation (LTP).     

On the cluster mechanism of diamond synthesis from different solid carbon forms

The cluster mechanism of diamond synthesis has been proposed. The mechanism is based on the concept of vibrational interactions between objects with the anomalously high Debye temperature. The estimates obtained for the crystal sizes are in good agreement with the experimental data on the dynamic and static syntheses of diamonds from different solid carbon forms such as organic materials, nanodiamonds, fullerite, graphite, and nanotubes.     

The connection between the two forms of perturbed sine-Gordon equations

A relationship between the first-order solutions of the two forms of perturbed sine-Gordon equations is established.     

Competition between two forms of ordering in finite Coulomb clusters

The lowest-energy state of spherical clusters made up of single-species charged particles in a three-dimensional confining potential is investigated by molecular dynamics simulations for a system size of 5 x 10(3) to 1.2 x 10(5). The energy per particle is compared between shell-structured clusters and spherical finite-bcc lattices with relaxed surfaces. The shell structure in the interior is the lowest-energy configuration for ion numbers lower than about 10(4), while for higher ion numbers, an interior with bcc ordering surrounded by a few shells on the outside has lower energy. The formation of a small bcc lattice (nucleation) in the shell-structured cluster of 2 x 10(4) ions is observed.     

Synchronization between different motifs

In this paper,we study the synchronization between different motifs.First,the synchronization between two networks with different topology structures and different dynamical behaviours is studied.With the open-plus-closed-loop(OPCL) method,conditions for two different networks to realize synchronization are given.Then based on the theoretical results achieved,the synchronization between different motifs is studied,which verifies the effectiveness and feasibility of the synchronization scheme.     

Common features of the amplitude-frequency characteristics of vowels in different forms of speech

According to classical concepts, the relationship between the first two formants is the feature that determines the identification of long vowels in speech. However, the characteristics of vowels may considerably vary depending on the conditions of their production. Thus, the aforementioned features that are valid for adult speech cannot be extended to speech signals with high fundamental frequencies, such as infant speech or singing. On the basis of the studies of preverbal infant vocalizations, singing, and speech imitation by talkingbirds, it is shown that the stable features of vowel-like sounds are the positions and amplitude ratios of the most pronounced spectral maxima (including those corresponding to the fundamental frequency). The results of the studies suggest that precisely these features determine the categorical identification of vowels. The role of the relationship between the frequency and amplitude characteristics in the vowel identification irrespective of the way the vowel is produced and the age and state of the speaker, as well as in the case of speech imitation by talkingbirds, is discussed.     

不同LET射线对细胞的生物学效应

以人肝癌细胞系和正常肝细胞系为材料,报道了不同传能线密度射线辐射引发细胞染色体原初断裂及24 h内的修复情况。 计算了相对生物学效应的值。 以L02染色体总断裂数量得出的RBE值96.05 keV/μm的12C6+ 为3.6, 512 keV/μm 36Ar18+ 为2.9。 而以7721染色体总断裂数量得出的RBE值: 96.05 keV/μm的12C6+ 为3.5,512keV/μm 36Ar18+也为2.9。用产生等点染色单体断裂计算,则RBE更高。对比得出,高LET对增加等点染色单体断裂量的作用要远远大于对增加染色单体断裂量的作用。等点染色单体的断裂修复难度要远远大于染色单体断裂的修复难度, 这也是高LET高致死率的一个重要原因。 Human hepatoma SMMC 7721 and normal liver L02 cells were irradiated with γ rays,12C6+ and 36Ar18+ ion beams at the Heavy Ion Research Facility in Lanzhou(HIRFL). We reported the kinetic repair of chromosome breaks of L02 and SMMC 7721 cells in 24 h of post irradiation time. The relative biological effectiveness(RBE) for inducing chromatid breaks were 3.6 for L02 and 3.5 for SMMC 7721 cell lines at the linear energy transfer(LET) peak of 96.55 keV/μm 12C6+ ions, and 2.9 (both of the two cell lines) at 512 keV/μm 36Ar18+ ions.It suggested that the RBE of isochromatid type breaks induced by 36Ar18+ was higher than those by 12C6+. We concluded that the high production of isochromatid type breaks, induced by the densely ionizing track structure, could be regarded as a signature of high LET radiation exposure.