1,758 research outputs found
Microscopic Description of Deeply Virtual Compton Scattering off Spin-0 Nuclei
We evaluate within a microscopic calculation the contributions of both
coherent and incoherent deeply virtual Compton scattering from a spin-0
nucleus. The coherent contribution is obtained when the target nucleus recoils
as a whole, whereas for incoherent scattering break-up configurations for the
final nucleus into a an outgoing nucleon and an system are considered.
The two processes encode different characteristics of generalized parton
distributions.Comment: 7 pages, 3 figure
Nuclear Medium Modifications of Hadrons from Generalized Parton Distributions
We study the structure of generalized parton distributions in spin 0 nuclei
within a microscopic approach for nuclear dynamics. GPDs can be used on one
side as tools to unravel the deep inelastic transverse structure of nuclei in
terms of both transverse spatial and transverse momentum degrees of freedom. On
the other, one can obtain information on GPDs themselves by observing how they
become modified in the nuclear environment. We derive the structure of the
nuclear deeply virtual Compton scattering tensor and generalized parton
distributions at leading order in in a field-theoretical framework. The
nuclear generalized parton distributions are calculated using a two step
process -- the convolution approach -- where the scattering process happens
from a quark inside a nucleon, itself inside a nucleus, disregarding final
state interactions with both the nuclear and nucleon debris. We point out that
details of the nuclear long range interactions such as two-body currents, can
be disregarded compared to the deep inelastic induced modifications of the
bound GPDs. We show how the pattern of nuclear modifications predicted, and in
particular the deviations of off-shell effects from the longitudinal
convolution provide clear signals to be sought in experimental measurements.
Finally, we find interesting relationships by studying Mellin moments in
nuclei: in particular we predict the -dependence for the -term of GPDs
within a microscopic approach, and the behavior with of the total momentum
carried by quarks in a nucleus. The latter provides an important element for
the evaluation of nuclear hadronization phenomena which are vital for
interpreting current and future data at RHIC, HERMES and Jefferson Lab.Comment: 29 pages, 10 figure
The Present status and the projected programme on niobium-tantalum metallurgy in India
Niobium and tantalum which belong to the family of ref-ractory rare metals, have assumed great strategic impo-rtance in present day material development programmes, specially in industries like chemical and nuclear engineering, electronics and aerospace. The use of niob-ium as ferroniobium contributing to carbide stabilisat-ion in stainless steel is well established and accounts for the major demand for niobium in the world today. At the same time, niobium-based alloys have been considered excellent for high temperature service, and in particular two alloys (i) SU-16 (Nb- 11 W- 3Mo -21-If-0 - 08C), and (ii) Nb-752 (Nb-IOW- 25Zr)'--have been developed for application in aerospace structure components. With its relatively low neutron absorption cross-section (Q8= I 1 barns), compatibility both with uranium fuels and liquid metal coolants, and good high temperature strength and fabrication characteristics, niobium is also an attra-ctive candidate for nuclear energy application, parti-cularly in fast reactors. Also, a zirconium-alloy conta-ining 2.5% of niobium is a potential competitor to
zircaloy for structural core components in water-cooled thermal reactor systems
Generalized Parton Distributions from Hadronic Observables: Zero Skewness
We propose a physically motivated parametrization for the unpolarized
generalized parton distributions. At zero value of the skewness variable,
, the parametrization is constrained by simultaneously fitting the
experimental data on both the nucleon elastic form factors and the deep
inelastic structure functions. A rich phenomenology can be addressed based on
this parametrization. In particular, we track the behavior of the average: {\it
i)} interparton distances as a function of the momentum fraction, , {\it
ii)} as a function of the four-momentum transfer, ; and {\it iii)} the
intrinsic transverse momentum as a function of . We discuss the
extension of our parametrization to where additional constraints
are provided by higher moments of the generalized parton distributions obtained
from {\it ab initio} lattice QCD calculations.Comment: 42 pages, 21 figure
Transport in bacteriophage P22-infected Salmonella typhimurium
There was rapid efflux of L-leucine, L-phenylalanine, and α-methyl-D-glucoside after infection of Salmonella typhimurium with the clear plaque mutant C1 of phage P22. The efflux was similar to that observed with cyanide or arsenate treatment except that there was partial recovery in the case of phage infection and almost complete recovery under the condition of lysogeny. There was no efflux after infection with the temperature-sensitive mutant ts16C1 at nonpermissive temperature. Superinfection of superinfection exclusion negative lysogen (sie A - sie B-) with C1 led to efflux, whereas the efflux was much less on superinfection of sie A+ Sie B+ lysogen. These results indicate that an effective injection process is enough to cause depression in the cellular transport processes
On the A-dependence of nuclear generalized parton distributions
We perform a microscopic evaluation of nuclear GPDs for spin-0 nuclei in the
framework of the Walecka model. We demonstrate that the meson (non-nucleon)
degrees of freedom dramatically influence nuclear GPDs, which is revealed in
the non-trivial and unexpected A-dependence of DVCS observables. In particular,
we find that the first moment of the nuclear D-term, d_A(0) ~ A^2.26, which
confirms the earlier prediction of M.Polyakov. We find that in the HERMES
kinematics, contrary to the free proton case, the nuclear meson degrees of
freedom in large nuclei enhance the nuclear DVCS amplitude which becomes
comparable to the Bethe-Heitler amplitude, and, thus, give the non-trivial
A-dependence to the DVCS asymmetries: as a function of the atomic number the
beam-charge asymmetry increases whereas the beam-spin asymmetry decreases
slowly.Comment: Final version published in J. Phys. G. 17 pages, 9 figure
Against the Odds: Psychomotor Development of Children Under 2 years in a Sudanese Orphanage.
Providing abandoned children the necessary medical and psychological care as possible after their institutionalization may minimize developmental delays. We describe psychomotor development in infants admitted to an orphanage in Khartoum, Sudan, assessed at admission and over an 18-month follow-up. Psychological state and psychomotor quotients were determined using a simplified Neonatal Behavior Assessment Scale (NBAS), the Brunet-Lezine and Alarm distress baby (ADBB) scale. From May-September 2005, 151 children were evaluated 2, 4, 9, 12 and 18 months after inclusion. At admission, ∼15% of children ≤1 month had a regulation impairment according to the NBAS, and 33.8% presented a distress state (ADBB score >5). More than 85% (129/151) recovered normal psychomotor development. The results of the program reinforce the importance of early detection of psychological disorders followed by rapid implementation of psychological case management to improve the development of young children in similar institutions and circumstances
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