Polarimetric constraints on the optical afterglow emission from GRB 990123

Polarization of the optical emission from GRB 990123 was measured on 24.17 January 1999 universal time with the Nordic Optical Telescope. An upper limit of 2.3% on the linear polarization was found. Accurate polarization measurements provide important clues to the blast wave geometry and magnetic field structure of gamma-ray bursts (GRBs). The lack of detectable polarization for GRB 990123 indicates that the optical afterglow was produced by a blast wave of unknown geometry with an insignificant coherent magnetic field or by a beamed outflow at high Lorentz factor seen at a small viewing angle. Such a collimated jet would help solve the problem of energy release in this exceptionally luminous cosmological burst.     

Observation of X-ray lines from a gamma-ray burst (GRB991216): evidence of moving ejecta from the progenitor

We report on the discovery of two emission features observed in the x-ray spectrum of the afterglow of the gamma-ray burst (GRB) of 16 December 1999 by the Chandra X-ray Observatory. These features are identified with the Ly(alpha) line and the narrow recombination continuum by hydrogenic ions of iron at a redshift z = 1.00 +/- 0.02, providing an unambiguous measurement of the distance of a GRB. Line width and intensity imply that the progenitor of the GRB was a massive star system that ejected, before the GRB event, a quantity of iron approximately 0.01 of the mass of the sun at a velocity approximately 0.1 of the speed of light, probably by a supernova explosion.     

Early optical polarization of a gamma-ray burst afterglow

We report the optical polarization of a gamma-ray burst (GRB) afterglow, obtained 203 seconds after the initial burst of gamma-rays from GRB 060418, using a ring polarimeter on the robotic Liverpool Telescope. Our robust (2sigma) upper limit on the percentage of polarization, less than 8%, coincides with the fireball deceleration time at the onset of the afterglow. The combination of the rate of decay of the optical brightness and the low polarization at this critical time constrains standard models of GRB ejecta, ruling out the presence of a large-scale ordered magnetic field in the emitting region.     

Decay of the GRB 990123 optical afterglow: implications for the fireball model

Broad-band (ultraviolet to near-infrared) observations of the intense gamma ray burst GRB 990123 started approximately 8.5 hours after the event and continued until 18 February 1999. When combined with other data, in particular from the Robotic Telescope and Transient Source Experiment (ROTSE) and the Hubble Space Telescope (HST), evidence emerges for a smoothly declining light curve, suggesting some color dependence that could be related to a cooling break passing the ultraviolet-optical band at about 1 day after the high-energy event. The steeper decline rate seen after 1.5 to 2 days may be evidence for a collimated jet pointing toward the observer.     

Discovery of a transient absorption edge in the X-ray spectrum of GRB 990705

We report the discovery of a transient equivalent hydrogen column density with an absorption edge at approximately 3.8 kiloelectron volts in the spectrum of the prompt x-ray emission of gamma-ray burst (GRB) 990705. This feature can be satisfactorily modeled with a photoelectric absorption by a medium located at a redshift of approximately 0.86 and with an iron abundance of approximately 75 times the solar one. The transient behavior is attributed to the strong ionization produced in the circumburst medium by the GRB photons. The high iron abundance points to the existence of a burst environment enriched by a supernova along the line of sight. The supernova explosion is estimated to have occurred about 10 years before the burst. Our results agree with models in which GRBs originate from the collapse of very massive stars and are preceded by a supernova event.     

Nitrogen dioxide in the stratosphere and troposphere measured by ground-based absorption spectroscopy

The NO(2) abundance in the stratosphere has been determined from ground-based spectra of the rising and setting sun and moon and of the twilight sky near 4500 angstroms. The spectra were taken at the Fritz Peak Observatory, at an altitude of 3 kilometers in the Colorado mountains. Separation of the stratospheric contribution requires observations at a relatively unpolluted site; direct measurement of the tropospheric absorption in the Colorado mountains often yields an upper limit on the tropospheric mixing ratio of 0.1 part per billion. The stratospheric NO(2) abundance is two to three times greater at night than during the day and increases significantly during the course of a sunlit day; these changes are related to photolytic decomposition of NO(2) and N(2)O(5) in the daytime stratosphere. Absorption by NO(3) was sought but not found; the results set an upper limit of 2 percent on the nighttime abundance ratio of NO(3) to NO(2) in the stratosphere.     

Selective Laser Photocatalysis of Bromine Reactions: Laser light excites gaseous bromine molecules to single bound quantum states near the dissociation continuum

The results have shown that selective excitation obtained with a tunable monochromatic laser is a useful technique for studying photochemical and energy transfer processes. A new phenomenon in the photochemistry of bromine was observed, in which bound excited molecules, and not atoms, were formed in the primary process. The mechanism of the subsequent reaction consists of collisional dissociation of the excited molecules into atoms, which then initiated free-radical chains. A quantitative estimate of the collisional electronic relaxation rate for excited bromine molecules was obtained, and a new upper limit to the continuous absorption strength at 14,400 cm(-1) was determined.     

树形管道模型原理

本文简介了树形管道模型的基本理论,并对若干问题进行了讨论。作者认为比管道长L将随分层厚度△Z的增大而增大,Yukihiro等[6]所给出的关系式L_a/L_b=b/a(L_a和L_b分别是△z=a和△z=b时的L值)是有疑问的。     

Magnetic resonance properties of some lunar material

Paramagnetic resonance spectra of Apollo 11 fines and rocks were measured at 9 and 35 gigahertz and at 4 degrees , 80 degrees , and 300 degrees K. At both frequencies the material has an intense absorption at g = 2, with a line width of approximately 950 gauss. Fe ions with strong exchange interactions produce this resonance. A comparison of the resonance absorption due to Fe(3+) showed that the energy of the crystal field interaction was approximately 0.1 per centimeter. Mn(2+) was identified in several samples, and an absorption at g = 1.89 was tentatively attributed to Ti(3+). The nuclear magnetic resonance spectra of (27)Al had a distribution of asymmetry parameters eta ranging from 0.25 to 0.75 and had nuclear quadrupole coupling constants e(2)qQ/h of approximately 3 megahertz.     

AlH2P3O10·2H2 O（Ⅰ）对水中Ni^2＋的吸附动力学和热力学研究

采用静态吸附法研究Al2O3-P2O5-H2O反应体系产物三聚磷酸二氢铝Ⅰ型二水物[AlH2P3O10.2H2O（Ⅰ）]吸附水中Ni2＋的动力学和热力学。考察了温度、浓度、粒径、pH和搅拌速度对吸附过程的影响,通过不同温度下的吸附等温热力学性能的变化,计算了吸附焓、吸附熵和自由能。结果表明,在试验范围内,AlH2P3O10.2H2O（Ⅰ）对Ni2＋的吸附符合Langmuir吸附等温方程式,过程受颗粒扩散控制,反应级数为1.88,298.15 K时的热力学数据为：Ea=11.561 kJ/mol,ΔH=35.75 kJ/mol,ΔS=190.58 J/（mol.K）,ΔG=-21.07 kJ/mol,吸附为自发的吸热过程,其吸附动力学总方程为：1-2/3x-（1-x）2/3=0.36r02C01.88exp（-11 561/RT）。     

高温胁迫对樟树光合性能的影响

光合作用是植物对环境变化最为敏感的生理过程。通过研究高温胁迫对樟树Cinnamomum camphora叶绿素荧光诱导动力学、气体交换速率和水分利用效率的影响,以期从光合作用的角度揭示高温对樟树的危害机制。结果表明:35和45℃高温胁迫后,樟树叶绿素荧光诱导动力学曲线O到P点的荧光强度均随胁迫增强而明显降低,同时诱导动力学参数单位反应中心吸收的光能总量、单位反应中心捕获的光能总量、单位反应中心内电子传递的量子产额、光合性能指数和单位吸收面积上天线色素能量吸收的驱动力均明显降低,其中在45℃时降至最低,与对照（25℃）相比分别降低了21.7%（P < 0.01）,17.6%（P < 0.01）,38.8%（P < 0.01）,60.2%（P < 0.01）和26.9%（P < 0.01）。35和45℃高温胁迫后,单位反应中心热耗散的能量明显升高,与对照相比分别增加了13.5%（P < 0.05）和78.4%（P < 0.01）;此外,樟树光合速率、气孔导度、蒸腾速率和水分利用效率亦均明显降低,其中最大光合速率分别降低了16.0%（P < 0.05）和44.6%（P < 0.01）。由此可见,高温胁迫可通过降低樟树的光能吸收、量子产量和电子传递,并促进吸收光能进行热耗散,降低光系统Ⅱ效率,进而减少同化力以降低光合速率。     

The morphological evolution of galaxies

Many galaxies have taken on their familiar appearance relatively recently. In the distant Universe, galaxy morphology deviates significantly (and systematically) from that of nearby galaxies at redshifts (z) as low as 0.3. This corresponds to a time approximately 3.5 x 10(9) years in the past, which is only approximately 25% of the present age of the Universe. Beyond z = 0.5 (5 x 10(9) years in the past), spiral arms are less well developed and more chaotic, and barred spiral galaxies may become rarer. At z = 1, around 30% of the galaxy population is sufficiently peculiar that classification on Hubble's traditional "tuning fork" system is meaningless. On the other hand, some characteristics of galaxies have not changed much over time. The space density of luminous disk galaxies has not changed significantly since z = 1, indicating that although the general appearance of these galaxies has continuously changed over time, their overall numbers have been conserved.     

基于固定化AChE的流动注射型酶传感器研究

以固定化鲅鱼脑组织乙酰胆碱酯酶[acetylcholinesterase,AChE(EC 3.1.1.7)]为识别元件,以pH电极为换能器,构建流动注射型AChE酶传感器.该传感器在以磷酸盐缓冲液为载液的条件下具有良好的重现性(RSD=1.427%,n=10)和敏感性,可实现对有机磷化合物的在线监测;对甲基对硫磷具有线性响应的浓度范围为4.29×10-10^-4.29×10^-8mol·L^-1,最低检测限为1.3×10^-     

高效液相色谱—电喷雾质谱联用法检测豆芽中残留的6-苄基腺嘌呤

采用高效液相色谱—质谱法测定豆芽中6-苄基腺嘌呤残留。均质后的黄豆芽样品经乙腈溶液提取、无水硫酸镁盐析分层后,取有机相测定。采用ZORBAX SB C18色谱柱,以甲醇+0.1%乙酸水溶液(体积比75∶25)的混合液为流动相,色谱分离后进入质谱检测。质谱采用电喷雾离子源(ESI),负离子模式,选择离子(SIM)m/z 224[M-H]-。在0.1 mg/kg添加浓度下,平均回收率(n=7)为89.0%~92.2%,相对标准偏差≤9.9%。方法检出限(S/N=3)0.0021 mg/kg,在0.08~2.0 mg/L范围内具有良好线性,相关系数R2=0.999。     

土壤无限制水分区间的修正研究

土壤无限制水分区间(NLWR)是指土壤水势、通气状况和机械阻力对作物生长发育没有限制作用的土壤水分含量区间。在保持其上限即土壤田间持水量或通气孔隙为10%时的土壤含水量不变的基础上,该研究对下限进行了修正,取土壤总水势为-0.3 MPa时的含水量或土壤机械阻力为0.85 MPa时的含水量作为NLWR的下限,代替原有的是永久萎蔫点或土壤机械阻力为2.0 MPa时的含水量。用上限的最小值减去下限的最大值,即可计算出NLWR。与原有的NLWR或土壤最小限制水分区间相比,修正后的NLWR更具有现实意义。NLWR为0时所对应的土壤容重(D b)称为临界容重(D b-thr),可以作为田间土壤物理质量管理的判断标准。当D bD b-thr时,土壤物理性质对作物产生阻碍作用,需进行土壤改良;当D bD b-thr时,只要土壤含水量处于NLWR之内,土壤物理性质对作物生长无影响,此时NLWR可以作为农田水分灌溉管理的依据。     

Hubble space telescope observations of comet p/shoemaker-levy 9 (1993e)

The Hubble Space Telescope observed the fragmented comet P/Shoemaker-Levy 9 (1993e) (P indicates that it is a periodic comet) on 1 July 1993. Approximately 20 individual nuclei and their comae were observed in images taken with the Planetary Camera. After subtraction of the comae light, the 11 brightest nuclei have magnitudes between approximately 23.7 and 24.8. Assuming that the geometric albedo is 0.04, these magnitudes imply that the nuclear diameters are in the range approximately 2.5 to 4.3 kilometers. If the density of each nucleus is 1 gram per cubic centimeter, the total energy deposited by the impact of these 11 nuclei into Jupiter's atmosphere next July will be approximately 4 x 10(30) ergs ( approximately 10(8) megatons of TNT). This latter number should be regarded as an upper limit because the nuclear magnitudes probably contain a small residual coma contribution. The Faint Object Spectrograph was used to search for fluorescence from OH, which is usually an excellent indicator of cometary activity. No OH emission was detected, and this can be translated into an upper limit on the water production rate of approximately 2 x 10(27) molecules per second.     

贵州湄潭茶区土壤-茶叶系统中微量元素富集规律与产地溯源

为了解贵州湄潭茶区土壤-茶叶系统中微量元素的迁移与特征规律,采集湄潭县洗马镇、鱼泉镇等12个村镇的茶叶与土壤,利用电感耦合等离子体发射光谱仪(ICP-OES)测定茶叶、土壤中11种微量元素(Ce、Co、Fe、La、Mg、Mn、Na、Ni、Pr、Se、Zn)的含量。结果表明:上述地区土壤Ni、Zn等重金属的平均含量低于国家限定标准,所测重金属中单项污染指数(P_i)≤1,地累计指数(I_geo)≤0,表明这些地区土壤均未受到污染,且湄潭茶区达到富硒土壤要求;但Co、Pr、Ni的污染指数接近污染值界限,建议茶区减少含有Co、Pr、Ni 3种元素的有毒有害物质排放,以便解决未来元素污染的隐患,保持土壤清洁状态;对照国家标准,湄潭茶叶重金属含量未超标,且湄潭部分茶区符合富硒茶叶要求;茶叶-土壤-pH值系统中,茶叶与土壤上下层大部分元素含量有正或负相关关系,上下层土壤pH值与其部分元素含量也有正或负相关关系,茶树中Mn元素富集能力较强,Mn元素的吸收与Mg、Na、Ni、Pr、Co、Se元素的吸收具有一定拮抗作用;采用主成分分析与典则判别分析探讨湄潭茶区土壤上下层以及茶叶特征规律,发现主成分分析和典则判别分析均可将12个茶区的茶叶、土壤各自区分,其不仅实现了不同茶区土壤的区分,而且相同茶区土壤上下层也得到区分,且典则判别分析结果图中数据点的聚集性更好,以上结果证实,湄潭茶区不同地域茶叶与土壤微量元素含量特征存在差异性,特征规律明显。系统地对湄潭茶区土壤-茶叶体系中微量元素的特征规律进行探究,可为贵州省湄潭茶区土壤-茶叶体系中微量元素富集、迁移规律,以及产地溯源提供依据。     

Is there any chlorine monoxide in the stratosphere?

A ground-based search for stratospheric chlorine monoxide was carried out during May and October 1981 with an infrared heterodyne spectrometer in the solar absorption mode. Lines due to stratospheric nitric acid and tropospheric carbonyl sulfide were detected at about 0.2 percent absorptance levels, but the expected 0.1 percent lines of chlorine monoxide in this same region were not seen. Stratospheric chlorine monoxide is less abundant by at least a factor of 7 than is indicated by in situ measurements, and the upper limit for the integrated vertical column density of chlorine monoxide is 2.3 x 10(13) molecules per square centimeter at the 95 percent confidence level. These results imply that the release of chlorofluorocarbons may be significantly less important for the destruction of stratospheric ozone than is currently thought.     

Determination of ultratrace cadmium in food and environmental samples by ETAAS after vapor generation and in situ preconcentration

A method is described for the determination of ultratrace cadmium by coupling a continuous flow vapor generation system with in situ preconcentration technique and electrothermal atomic absorption spectrometry (ETAAS). A graphite tube coated with Ir as permanent chemical modifier was used for trapping cadmium vapor species. The effects of the flow rates of carrier gas and sample injection in vapor generation systems on the trapping measurement for cadmium were respectively investigated. Graphite tubes with different characteristic surfaces were comparatively studied for trapping cadmium vapor. The experimental results showed that the permanent chemical modifier of Ir is an alternative to the thermolabile modifier of Pd for simplifying the trapping measurement. The trapping efficiency of cadmium on the graphite tube coated with Ir was estimated. The trapping temperature and time were also investigated. A detection limit (3σ) of 0.005 μg·L⁻¹ was obtained for this proposed method. The relative standard deviation (RSD) was 1.4% for 0.5 μ·L⁻¹ of Cd (n = 11). This method can be applied to the determination of ultratrace cadmium in food and environmental samples with good agreement between the certified and found values.     

A photoinduced persistent structural transformation of the special pair of a bacterial reaction center

Structural modification of photosynthetic reaction centers is an important approach for understanding their charge-separation processes. An unprecedented persistent structural transformation of the special pair (dimer) of bacteriochlorophyll molecules can be produced by light absorption alone. The nonphotochemical hole-burned spectra for the reaction center of Rhodopseudomonas viridis show that the phototransformation leads to a red shift of 150 wave numbers for the special pair's lowest energy absorption band, P960, and a comparable blue shift for a state at 850 nanometers, which can now be definitively assigned as being most closely associated with the upper dimer component. Additional insights on excited-state electronic structure include the identification of a new state.