巴基斯坦国日本金线鱼（Nemipterus japonicus）种群动力学的研究     

Kalhoro Muhsan Ali  刘群  Memon Khadim Hussain  Chang Mohammad Saleem  张魁 《海洋学报(英文版)》2014,33(10):49-57

Japanese threadfin bream Nemipterus japonicus(Bloch, 1791) is among the most abundant and commercially important species in Pakistan. From the coast of Pakistan, four demersal trawl surveys in October–November 2009 and May–June, August, October and November in 2010 were carried out. The purpose of this study is to estimate the population dynamics and status of the stock of the N. japonicus from Pakistani waters based on the research trawl surveys from the research area. The data consist of n=784 length-weight pairs and n=7 530 length frequency with the maximum length and weight of 29 cm and 358 g respectively. The length frequency data were analyzed using ELEFAN method in FiSAT computer package. The parameters of length and weight relationship were b=2.778, a=0.032 and R2=0.973. The estimated von Bertalanffy growth function parameters were L∞=30.45 cm, K=0.270 year-1. Based on length-converted catch curve analysis the total mortality(Z) during this study was estimated at 0.960 year-1. The natural mortality coefficient(M) was 0.74 year-1 using Pauly's equation(the annual average sea surface temperature was 27°C), therefore, the fishing mortality coefficients(F) were 0.22 year-1. The yield per recruit analysis indicated that when tc was 2, Fmax was estimated at 1.2 and F0.1 at 1.1. When tc was 1, Fmax was estimated at 0.95 and F0.1 at 0.8. Because current age at first capture is about 1 year and Fcurrent was 0.22, Fcurrent is smaller than F0.1 and Fmax, which indicated that the fishery is about in a safe condition. When using Gulland(1971) biological reference point, Fopt was equals to M(0.74). The current fishing mortality rate of 0.22 was smaller than the target biological reference point.  相似文献   

TTG-type plutonic rocks formed in a modern arc batholith by hydrous fractionation in the lower arc crust     

Oliver Jagoutz  Max W. Schmidt  Andreas Enggist  Jean-Pierre Burg  Dawood Hamid  Shahid Hussain 《Contributions to Mineralogy and Petrology》2013,166(4):1099-1118

We present the geochemistry and intrusion pressures of granitoids from the Kohistan batholith, which represents, together with the intruded volcanic and sedimentary units, the middle and upper arc crust of the Kohistan paleo-island arc. Based on Al-in-hornblende barometry, the batholith records intrusion pressures from ~0.2 GPa in the north (where the volcano-sedimentary cover is intruded) to max. ~0.9 GPa in the southeast. The Al-in-hornblende barometry demonstrates that the Kohistan batholith represents a complete cross section across an arc batholith, reaching from the top at ~8–9 km depth (north) to its bottom at 25–35 km (south-central to southeast). Despite the complete outcropping and accessibility of the entire batholith, there is no observable compositional stratification across the batholith. The geochemical characteristics of the granitoids define three groups. Group 1 is characterized by strongly enriched incompatible elements and unfractionated middle rare earth elements (MREE)/heavy rare earth element patterns (HREE); Group 2 has enriched incompatible element concentrations similar to Group 1 but strongly fractionated MREE/HREE. Group 3 is characterized by only a limited incompatible element enrichment and unfractionated MREE/HREE. The origin of the different groups can be modeled through a relatively hydrous (Group 1 and 2) and of a less hydrous (Group 3) fractional crystallization line from a primitive basaltic parent at different pressures. Appropriate mafic/ultramafic cumulates that explain the chemical characteristics of each group are preserved at the base of the arc. The Kohistan batholith strengthens the conclusion that hydrous fractionation is the most important mechanism to form volumetrically significant amounts of granitoids in arcs. The Kohistan Group 2 granitoids have essentially identical trace element characteristics as Archean tonalite–trondhjemite–granodiorite (TTG) suites. Based on these observations, it is most likely that similar to the Group 2 rocks in the Kohistan arc, TTG gneisses were to a large part formed by hydrous high-pressure differentiation of primitive arc magmas in subduction zones.  相似文献   

Dynamo processes and activity cycles of the active stars AB Doradus, LQ Hydrae and HR 1099     

J.-F. Donati  A. Collier Cameron  M. Semel  G. A. J. Hussain  P. Petit  B. D. Carter  S. C. Marsden  M. Mengel  A. López Ariste  S. V. Jeffers  D. E. Rees 《Monthly notices of the Royal Astronomical Society》2003,345(4):1145-1186

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Statistical downscaling and future scenario generation of temperatures for Pakistan Region     

Dildar Hussain Kazmi  Jianping Li  Ghulam Rasul  Jiang Tong  Gohar Ali  Sohail Babar Cheema  Luliu Liu  Marco Gemmer  Thomas Fischer 《Theoretical and Applied Climatology》2015,120(1-2):341-350

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Two dimensional ion acoustic shocks in electron-positron-ion plasmas with warm ions,and q-nonextensive distributed electrons and positrons     

S. Hussain  Hafeez Ur-Rehman  S. Mahmood 《Astrophysics and Space Science》2014,351(2):573-580

Two dimensional ion acoustic shocks in electron-positron-ion (e-p-i) plasma with warm ions, and nonthermal electrons and positrons following the q-nonextensive velocity distribution are studied in the presence of weak transverse perturbations. The kinematic viscosity of warm ions is included for the dissipation in the plasma system. Kadomtsev–Petviashvili–Burgers (KPB) equation is derived by using reductive perturbation method in small amplitude limit and its analytical solution is also presented. The effects of variations of positrons concentration, q-indices of electrons and positrons, ion temperature and kinematic viscosity of ions, on the propagation characteristic of two dimensional shock profile are also discussed.  相似文献   

UVMag: stellar formation,evolution, structure and environment with space UV and visible spectropolarimetry     

C. Neiner  D. Baade  A. Fullerton  C. Gry  G. Hussain  A. Lèbre  J. Morin  P. Petit  J. O. Sundqvist  A. ud-Doula  A. A. Vidotto  G. A. Wade  The UVMag consortium 《Astrophysics and Space Science》2014,354(1):215-227

Important insights into the formation, structure, evolution and environment of all types of stars can be obtained through the measurement of their winds and possible magnetospheres. However, this has hardly been done up to now mainly because of the lack of UV instrumentation available for long periods of time. To reach this aim, we have designed UVMag, an M-size space mission equipped with a high-resolution spectropolarimeter working in the UV and visible spectral range. The UV domain is crucial in stellar physics as it is very rich in atomic and molecular lines and contains most of the flux of hot stars. Moreover, covering the UV and visible spectral domains at the same time will allow us to study the star and its environment simultaneously. Adding polarimetric power to the spectrograph will multiply tenfold the capabilities of extracting information on stellar magnetospheres, winds, disks, and magnetic fields. Examples of science objectives that can be reached with UVMag are presented for pre-main sequence, main sequence and evolved stars. They will cast new light onto stellar physics by addressing many exciting and important questions. UVMag is currently undergoing a Research & Technology study and will be proposed at the forthcoming ESA call for M-size missions. This spectropolarimeter could also be installed on a large UV and visible observatory (e.g. NASA’s LUVOIR project) within a suite of instruments.  相似文献   

A simple model for the evolution of supermassive black holes and the quasar population     

Asim Mahmood  Julien E. G. Devriendt  Joseph Silk 《Monthly notices of the Royal Astronomical Society》2005,359(4):1363-1378

An empirically motivated model is presented for accretion-dominated growth of supermassive black holes (SMBH) in galaxies, and the implications are studied for the evolution of the quasar population in the Universe. We investigate the core aspects of the quasar population, including space density evolution, evolution of the characteristic luminosity, plausible minimum masses of quasars, the mass function of SMBH and their formation epoch distribution. Our model suggests that the characteristic luminosity in the quasar luminosity function arises primarily as a consequence of a characteristic mass scale above which there is a systematic separation between the black hole and the halo merging rates. At lower mass scales, black hole merging closely tracks the merging of dark haloes. When combined with a declining efficiency of black hole formation with redshift, the model can reproduce the quasar luminosity function over a wide range of redshifts. The observed space density evolution of quasars is well described by formation rates of SMBH above  ∼10⁸  M_⊙  . The inferred mass density of SMBH agrees with that found independently from estimates of the SMBH mass function derived empirically from the quasar luminosity function.  相似文献   

New data on the Indus Kohistan seismic zone and its extension into the Hazara-Kashmir Syntaxis, NW Himalayas of Pakistan     

MonaLisa  Azam A. Khwaja  M. Qasim Jan  Robert S. Yeats  Ahmad Hussain  Shahid A. Khan 《Journal of Seismology》2009,13(4):665-665

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Ion acoustic solitons in negative ion plasmas with superthermal electrons     

S. Hussain  N. Akhtar  S. Mahmood 《Astrophysics and Space Science》2012,338(2):265-270

Korteweg-de Vries (KdV) equation for electrostatic wave in an unmagnetized negative ion plasma with superthermal electrons is derived using reductive perturbation technique. A generalized Lorentzian distribution (kappa distribution) is assumed for the electrons. The influence of spectral index (kappa) on the soliton is discussed in the presence of the negative ions. It is found that different plasma parameters such as (negative ion temperature, positive ion temperature, negative ion concentration, mass ratio of positive to negative ion) in the presence of superthermal electrons modify the ion acoustic solitary wave structure significantly.  相似文献   

Understanding the enhanced aqueous solubility of styrene by terrestrial dissolved organic matter using stable isotope mass balance and FTIR     

Hussain A.N. Abdulla  Robert F. Dias  Elizabeth C. Minor 《Organic Geochemistry》2009,40(5):547-552

We present a new stable isotope mass balance method for measuring the enhanced aqueous solubility of specific organic compounds in the presence of natural dissolved organic matter (DOM). It involves interfacing a standard dissolved organic carbon (DOC) analyzer with a stable isotope ratio monitoring system, is applicable to a wide range of model organic compounds and can be tuned to provide maximum precision for a given range of compound solubility and initial natural DOC concentration. Using ¹³C-labeled styrene as a model compound, we applied the method to investigate the reactivity of Dismal Swamp DOM as a function of season, nominal molecular size and chemical composition as determined using Fourier Transform Infrared Spectroscopy (FTIR). The solubility enhancement of styrene ranged from 23% to 118% relative to deionized water, while DOC-normalized enhancements varied from about 0.04 to 0.35 μM styrene/μM DOC as a function of season and nominal molecular weight. Statistical analysis of FTIR spectra reveals a strong positive correlation between the styrene concentration and the carboxyl content of the natural DOM. Reactivity differences between high molecular weight (HMW), low molecular weight (LMW) and total DOM samples are consistent with potential variations in their higher order structures.  相似文献