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51.
Anindya Datta Amitava Raychaudhuri Sreerup Raychaudhuri Surajit Chakrabarti 《Zeitschrift fur Physik C Particles and Fields》1996,72(3):449-460
Many extensions of the Standard Model includeSU(2) L ×U(1) Y singlet higgs bosons,h 0, and also vector-like fermions which couple to it. The production and detection possibilities of such singlet neutral scalars at hadron colliders are considered for different scenarios of vectorlike fermions. We find that for some values of masses and couplings, detection at the CERN large hadron collider (LHC) appears to be a distinct possibility, while at the Fermilab Tevatron upgrade theh 0 might be observed only in very favourable circumstances. 相似文献
52.
R. Chattopadhyay 《Journal of Optimization Theory and Applications》1972,9(3):216-219
This paper presents a method for solving a class of constrained optimization problems in finite-dimensional spaces. This type of problem usually arises in connection with parameter optimization in engineering design. Most often, these problems consist of incorporating upper and/or lower bounds on the variables in otherwise unconstrained optimization problems. The proposed method replaces the original optimization problem withm constraints (m>1) by a sequence of optimization problems with one constraint only. The theory behind this method is discussed in the subsequent sections.This research was supported by NSF Grant No. GK-4984. 相似文献
53.
Chattopadhyay J Sadana AK Liang F Beach JM Xiao Y Hauge RH Billups WE 《Organic letters》2005,7(19):4067-4069
[reaction: see text] Carbon nanotube salts prepared by treating single-wall carbon nanotubes (SWNTs) with lithium in liquid ammonia react readily with aryl iodides to give SWNTs functionalized by aryl groups. 相似文献
54.
Surajit?Dasgupta Neven?Bilic Tapas?K.?DasEmail author 《General Relativity and Gravitation》2005,37(11):1877-1890
We demonstrate that a spherical accretion onto astrophysical black holes, under the influence of Newtonian or various post-Newtonian
pseudo-Schwarzschild gravitational potentials, may constitute a concrete example of classical analogue gravity naturally found
in the Universe. We analytically calculate the corresponding analogue Hawking temperature as a function of the minimum number
of physical parameters governing the accretion flow. We study both the polytropic and the isothermal accretion. We show that
unlike in a general relativistic spherical accretion, analogue white hole solutions can never be obtained in such post-Newtonian
systems. We also show that an isothermal spherical accretion is a remarkably simple example in which the only one information–the
temperature of the fluid, is sufficient to completely describe an analogue gravity system. For both types of accretion, the
analogue Hawking temperature may become higher than the usual Hawking temperature. However, the analogue Hawking temperature
for accreting astrophysical black holes is considerably lower compared with the temperature of the accreting fluid. 相似文献
55.
Adams J Adler C Aggarwal MM Ahammed Z Amonett J Anderson BD Anderson M Arkhipkin D Averichev GS Badyal SK Balewski J Barannikova O Barnby LS Baudot J Bekele S Belaga VV Bellwied R Berger J Bezverkhny BI Bhardwaj S Bhaskar P Bhati AK Bichsel H Billmeier A Bland LC Blyth CO Bonner BE Botje M Boucham A Brandin A Bravar A Cadman RV Cai XZ Caines H Calderón de la Barca Sánchez M Carroll J Castillo J Castro M Cebra D Chaloupka P Chattopadhyay S Chen HF Chen Y Chernenko SP Cherney M Chikanian A Choi B 《Physical review letters》2004,92(17):171801
Measurements of the production of forward high-energy pi(0) mesons from transversely polarized proton collisions at sqrt[s]=200 GeV are reported. The cross section is generally consistent with next-to-leading order perturbative QCD calculations. The analyzing power is small at x(F) below about 0.3, and becomes positive and large at higher x(F), similar to the trend in data at sqrt[s]< or =20 GeV. The analyzing power is in qualitative agreement with perturbative QCD model expectations. This is the first significant spin result seen for particles produced with p(T)>1 GeV/c at a polarized proton collider. 相似文献
56.
We report measurements of birefringence
of several nematic liquid crystals having transverse as well as longitudinal dipole moments in thin (1.4 to
) and thick (7 to
cells. Rubbed polyimide-coated glass plates are used to get planar alignment of the nematic director in these cells. We find significant enhancement (6 to
) of
(
, where S is the orientational order parameter) in thin cells in all compounds with aromatic cores even at temperatures far (
C) below the nematic-isotropic transition point. The enhancement is larger in compounds having several phenyl rings and lower if the number of phenyl rings is reduced. In a compound that does not have an aromatic core no significant enhancement is observed, implying that the strength of the surface potential depends on the aromaticity of the cores. Assuming a perfect orientational order at the surface, calculations based on the Landau-de Gennes theory show that the thickness averaged enhancement of S is sharply reduced as the temperature is lowered in the nematic phase. The measured order parameter S is further enhanced in thin cells because of the stiffening of the elastic constant which reduces the thermal fluctuations of the nematic director. The combined effect is however too small at low temperatures to account for the experimental data.Received: 22 February 2004, Published online: 24 May 2004PACS:
61.30.-v Liquid crystals - 61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems - 61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitionsSurajit Dhara: Present address: Department of Physics, Birla Institute of Technology and Science, Pilani 333 031, India. 相似文献
57.
58.
J. W. Kooi G. Chattopadhyay M. Thielman T. G. Phillips R. Schieder 《International Journal of Infrared and Millimeter Waves》2000,21(5):689-716
There is a strong interest in the submillimeter astronomy community to increase the IF bandwidth of SIS receivers in order to better facilitate broad spectral linewidth and continuum observations of extragalactic sources. However, with an increase in receiver IF bandwidth there is a decrease in the mixer stability. This in turn effects the integration efficiency and quality of the measurement. In order to better understand the noise mechanisms responsible for reducing the receiver stability, we employed a technique first described by D.W. Allan and later elaborated upon by Schieder et al. In this paper we address a variety of factors that degrade the noise stability of SIS receivers. The goal of this exercise is to make recommendations aimed at maximizing SIS receiver stability. 相似文献
59.
Sk.F. Ahmed P.K. Ghosh S. Khan M.K. Mitra K.K. Chattopadhyay 《Applied Physics A: Materials Science & Processing》2007,86(1):139-143
We have observed low-macroscopic field electron emission from wide bandgap nanocrystalline Al doped SnO2 thin films deposited on glass substrates. The emission properties have been studied for different anode-sample spacings and for different Al concentrations in the films. The turn-on field and approximate work function were calculated and we have tried to explain the emission mechanism from this. The turn-on field was found to vary in the range 5.6–7.5 V/μm for a variation of anode sample spacing from 80–120 μm. The turn-on field was also found to vary from 4.6–5.68 V/μm for a fixed anode-sample separation of 80 μm with a variation of Al concentration in the films 8.16–2.31%. The Al concentrations in the films have been measured by energy dispersive X-ray analysis. Optical transmittance measurement of the films showed a high transparency with a direct bandgap ∼3.98 eV. Due to the wide bandgap, the electron affinity of the film decreased. This, along with the nanocrystalline nature of the films, enhanced the field emission properties. PACS 81.20.Fw; 61.10.-i; 79.70.+q 相似文献
60.
Surajit Saha Surjeet Singh R. Suryanarayanan A.K. Sood 《Journal of solid state chemistry》2011,184(8):2204-2208
Here we report a temperature-dependent Raman study of the pyrochlore “dynamic spin-ice” compound Pr2Sn2O7 and compare the results with its non-pyrochlore (monoclinic) counterpart Pr2Ti2O7. In addition to phonon modes, we observe two bands associated with electronic Raman scattering involving crystal field transitions in Pr2Sn2O7 at ∼135 and 460 cm−1 which couple strongly to phonons. Anomalous temperature dependence of phonon frequencies that are observed in pyrochlore Pr2Sn2O7 are absent in monoclinic Pr2Ti2O7. This, therefore, confirms that the strong phonon-phonon anharmonic interactions, responsible for the temperature-dependent anomalous behavior of phonons, arise due to the inherent vacant sites in the pyrochlore structure. 相似文献