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Search Results: 1 - 10 of 1837 matches for " ABHIJIT DATTA "
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Effects of SO(10) D-Term on Yukawa Unification and Unstable Minima of the Supersymmetric Scalar Potential
Amitava Datta,Abhijit Samanta
Physics , 2001, DOI: 10.1088/0954-3899/29/12/004
Abstract: We study the effects of SO(10) D-terms on the allowed parameter space (APS) in models with $t - b - \tau$ and $b - \tau$ Yukawa unifiction. The former is allowed only for moderate values of the D-term, if very precise ($\le$ 5%) unification is required. Next we constrain the parameter space by looking for different dangerous directions where the scalar potential may be unbounded from below (UFB1 and UFB3). The common trilinear coupling $A_0$ plays a significant role in constraing the APS. For very precise $t - b - \tau$ Yukawa unification, $-m_{16} < or \approx A_0 < or \approx m_{16}$ can be probed at the LHC, where $m_{16}$ is the common soft breaking mass for the sfermions. Moreover, an interesting mass hierarchy with very heavy sfermions but light gauginos, which is strongly disfavoured in models without D-terms, becomes fairly common in the presence of the D-terms. The APS exhibits interesting characteristics if $m_{16}$ is not the same as the soft breaking mass $m_{10}$ for the Higgs sector. In $b - \tau$ unification models with D-terms, the APS consistent with Yukawa unification and radiative electroweak symmetry breaking, increases as the UFB1 constraint becomes weaker. However for $A_0 \leq 0$, a stronger UFB3 condition still puts, for a given $m_{16}$, a stringent upper bound on the common gaugino mass ($m_{1/2}$) and a lower bound on $m_{16}$ for a given $m_{1/2}$. The effects of sign of $\mu$ on Yukawa unification and UFB constraints are also discussed.
Electroweak Precision Data, Light Sleptons and Stability of the SUSY Scalar Potential
Amitava Datta,Abhijit Samanta
Physics , 2001, DOI: 10.1016/S0370-2693(01)01490-3
Abstract: The light slepton-sneutrino scenario with non-universal scalar masses at the GUT scale is preferred by the electroweak precision data. Though a universal soft breaking mass at or below the Plank scale can produce the required non-universality at the GUT scale through running, such models are in conflict with the stability of the electroweak symmetry breaking vacuum. If the supergravity motivated idea of a common scalar mass at some high scale along with light sleptons is supported by future experiments that may indicate that we are living in a false vacuum. In contrast SO(10) D-terms, which may arise if this GUT group breaks down directly to the Standard Model, can lead to this spectrum with many striking phenomenological predictions, without jeopardizing vacuum stability.
Structural Analysis of Predicted HIV-1 Secis Elements  [PDF]
Paushali Roy, Sayak Ganguli, Pooja Sharma, Protip Basu, Abhijit Datta
World Journal of AIDS (WJA) , 2011, DOI: 10.4236/wja.2011.14030
Abstract: Incorporation of Selenocysteine into protein requires an RNA structural motif, SECIS (Selenocysteine insertion sequence) element that, along with other factors, demarcates UGA-Sec from the UGA termination codon, for expression of Selenoproteins (in case of eukaryotes). It has been predicted that during HIV infection, several functional viral selenoproteins are expressed and synthesis of these viral selenoproteins deplete the selenium level of the host. It might be that even the viral genome has the SECIS elements in their Selenoprotein mRNA, and during infection, the host cellular machinery is transformed in such a way that the human Sec tRNA binds to the viral Selenoprotein mRNA, instead of binding to its own Selenoprotein mRNA, thus leading to expression of viral selenoproteins. This hypothesis was tested in this study by identifying the SECIS elements in the HIV-1 genome and further predicting their secondary and tertiary structures. We then tried to dock these tertiary structures with human Sec tRNA. Here we report putatively the presence of 3215 SECIS elements in the HIV-1 genome and that the human Sec tRNAsec binds to the viral SECIS elements present in the viral selenoprotein mRNA. Based on an earlier finding, it was observed that atoms of A8 and U9, which present in human Sec tRNA, are the possible key sites for binding.
Antagomirbase- a putative antagomir database
Sayak Ganguli*,Sanga Mitra,Abhijit Datta
Bioinformation , 2011,
Abstract: The accurate prediction of a comprehensive set of messenger putative antagomirs against microRNAs (miRNAs) remains an open problem. In particular, a set of putative antagomirs against human miRNA is predicted in this current version of database. We have developed Antagomir database, based on putative antagomirs-miRNA heterodimers. In this work, the human miRNA dataset was used as template to design putative antagomirs, using GC content and secondary structures as parameters. The algorithm used predicted the free energy of unbound antagomirs. Although in its infancy the development of antagomirs, that can target cell specific genes or families of genes, may pave the way forward for the generation of a new class of therapeutics, to treat complex inflammatory diseases. Future versions need to incorporate further sequences from other mammalian homologues for designing of antagomirs for aid in research.
Molecular modeling of DICER and identification of phosphorylation sites
Priyanka Dhar*,Abhijit Datta,Sayak Ganguli
Bioinformation , 2010,
Abstract: RNA interference (RNAi) is a post-transcriptional process initiated by double-stranded RNA molecules that degrade a complementary target RNA. In the first step, long double-stranded RNA molecules are chopped into shorter duplexes by an endonuclease dubbed DICER. This work focused on the identification of phosphorylation sites in DICER and proceeded towards comparative modeling. The domain of unknown function in DICER showed homology with the chromatin remodeling protein domains. This suggests that DICER may also perform chromatin remodeling. The Ramachandran analysis revealed that the models had 96% residues in the permissible regions and could be used for future ligand binding studies.
INHIBITING H5N1 HAEMAGGLUTININ WITH SMALL MOLECULE LIGANDS
ADITI GANGOPADHYAY,SAYAK GANGULI,ABHIJIT DATTA
International Journal of Bioinformatics Research , 2011,
Abstract: Mutations in the avian influenza virus can create new pathogenic strains, which can cause futurepandemics. Targeting the surface haemagglutinin can inhibit viral fusion and consequent entry. The effects of 27single and double point mutations on the properties of the H5 haemagglutinin were studied. These mutations werethen introduced individually in the PDB file of the H5, to generate mutants. 13 herbal and non-herbal lead inhibitorsof H5 were screened and docked with the wild type and mutant haemagglutinins to obtain a comparative dockingprofile. The nature of the interactions of the inhibitors were analysed, and the binding residues determined. Thelatter further revealed that certain mutations in HA might be affecting inhibitor binding
Identification of regulatory sequence signatures in microRNA precursors implicated in neurological disorders  [PDF]
Sayak Ganguli, Sasti Gopal Das, Hirak Jyoti Chakraborty, Sohini Gupta, Abhijit Datta
Advances in Bioscience and Biotechnology (ABB) , 2013, DOI: 10.4236/abb.2013.45A003
Abstract:

MicroRNAs have emerged as one of the major classes of non-coding RNAs. Recent reports have placed them in high abundance in the nervous system, having key roles in development. Neurological disorders such as Parkinson’s disease, Alzheimer’s disease as well as Huntington disease have also been studied and several microRNAs associated with diseases pathogenesis have been identified. Various such findings indicate differential expression levels of many of these microRNAs. Such changes in the expression levels not only indicate towards a control of the biogenesis of these microRNAs but also indicate towards critical yet unelucidated roles of regulatory proteins, which probably act in concert to control the production or maturation of these molecules. In this work, a collection of overrepresented regulatory motif signatures were identified in the DNA and RNA sequences of the precursor microRNAs. The identification of such regulatory sequence signatures promises to provide new insights into many facets of microRNA regulation and neurological disorders.

Yukawa Unification and Unstable Minima of the Supersymmetric Scalar Potential
Amitava Datta,Anirban Kundu,Abhijit Samanta
Physics , 2000, DOI: 10.1103/PhysRevD.63.015008
Abstract: Motivated by the possibilities of $b-\tau$ or $t-b-\tau$ Yukawa unification in the supersymmetric Grand Unified Theories, we consider the dangerous directions of the supersymmetric potential for large values of $\tan\beta (\geq 30)$, in two versions of the minimal supergravity model with and without common soft breaking scalar masses at the GUT scale, where the potential may become unbounded from below. We find that for the common trilinear coupling $A_0 \leq 0$ the requirement of $b-\tau$ unification in conjunction with the stability condition on the potential yields highly restrictive sparticle spectra with upper, and in many cases, lower bounds stronger than the available experimental lower bounds, on the soft SUSY breaking common scalar mass and the common gaugino mass. Over a significant region of the parameter space, the model becomes even more restrictive if the common sfermion soft mass is different from the soft mass for the Higgs sector. We also find that the bulk of this restricted parameter space can be probed at the LHC. Im models with $t-b-\tau$ Yukawa unification, $A_0 \leq 0$ is ruled out from potential constraints.
Enhanced magnetism of Cu$_n$ clusters capped with N and endohedrally doped with Cr
Soumendu Datta,Radhashyam Banerjee,Abhijit Mookerjee
Physics , 2015, DOI: 10.1063/1.4905481
Abstract: The focus of our work is on the production of highly magnetic materials out of Cu clusters. We have studied the relative effects of N-capping as well as N mono-doping on the structural stability and electronic properties of the small Cu clusters using first principles density functional theory based electronic structure calculations. We find that the N-capped clusters are more promising in producing giant magnetic moments, such as 14 $\mu_B$ for the Cu$_6$N$_6$ cluster and 29 $\mu_B$ for the icosahedral Cu$_{13}$N$_{12}$ clusters. This is accompanied by a substantial enhancement in their stability. We suggest that these giant magnetic moments of the capped Cu$_n$ clusters have relevance to the observed room temperature ferromagnetism of Cu doped GaN. For cage-like hollow Cu-clusters, an endohedral Cr-doping together with the N-capping appears as the most promising means to produce stable giant magnetic moments in the copper clusters.
New Bounds on Slepton and Wino Masses in Anomaly Mediated Supersymmetry Breaking Models
Amitava Datta,Anirban Kundu,Abhijit Samanta
Physics , 2001, DOI: 10.1103/PhysRevD.64.095016
Abstract: We show how the spectrum of the minimal anomaly-mediated supersymmetry breaking model can be constrained from the condition that the electroweak symmetry breaking minimum of the scalar potential is the deepest point in the field space. Applying the current experimental bounds and scanning over the whole parameter space, we rule out selectrons below 378 GeV and staus below 269 GeV, the numbers having a modest uncertainty. We also find a new upper bound on the wino-like chargino mass for a given slepton mass. This rules out the possibility of slepton pair production at ongoing or upcoming colliders like the Tevatron or the Next Linear Collider at $\sqrt{s}=500$ GeV, where pair production of charginos may be the only available signal.
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