1,007 research outputs found
Detection of SUSY Signals in Stau Neutralino Co-annihilation Region at the LHC
We study the prospects of detecting the signal in the stau neutralino
co-annihilation region at the LHC using tau leptons. The co-annihilation signal
is characterized by the stau and neutralino mass difference (dM) to be 5-15 GeV
to be consistent with the WMAP measurement of the cold dark matter relic
density as well as all other experimental bounds within the minimal
supergravity model. Focusing on tau's from neutralino_2 --> tau stau --> tau
tau neutralino_1 decays in gluino and squark production, we consider inclusive
MET+jet+3tau production, with two tau's above a high E_T threshold and a third
tau above a lower threshold. Two observables, the number of opposite-signed tau
pairs minus the number of like-signed tau pairs and the peak position of the
di-tau invariant mass distribution, allow for the simultaneous determination of
dM and M_gluino. For dM = 9 GeV and M_gluino = 850 GeV with 30 fb^-1 of data,
we can measure dM to 15% and M_gluino to 6%.Comment: 4 pages LaTex, 3 figures. To appear in Proceedings of SUSY06, the
14th International Conference on Supersymmetry and the Unification of
Fundamental Interactions, UC Irvine, California, 12-17 June 2006. A typo in a
reference is correcte
Lithium and magnetic fields in giants. HD 232862 : a magnetic and lithium-rich giant star
We report the detection of an unusually high lithium content in HD 232862, a
field giant classified as a G8II star, and hosting a magnetic field. With the
spectropolarimeters ESPaDOnS at CFHT and NARVAL at TBL, we have collected high
resolution and high signal-to-noise spectra of three giants : HD 232862, KU Peg
and HD 21018. From spectral synthesis we have inferred stellar parameters and
measured lithium abundances that we have compared to predictions from
evolutionary models. We have also analysed Stokes V signatures, looking for a
magnetic field on these giants. HD 232862, presents a very high abundance of
lithium (ALi = 2.45 +/- 0.25 dex), far in excess of the theoretically value
expected at this spectral type and for this luminosity class (i.e, G8II). The
evolutionary stage of HD 232862 has been precised, and it suggests a mass in
the lower part of the [1.0 Msun ; 3.5 Msun ] mass interval, likely 1.5 to 2.0
solar mass, at the bottom of the Red Giant Branch. Besides, a time variable
Stokes V signature has been detected in the data of HD 232862 and KU Peg,
pointing to the presence of a magnetic field at the surface of these two
rapidly rotating active stars.Comment: 11 pages, 9 figures ; accepted by Astronomy and Astrophysic
Topological Entropy of Braids on the Torus
A fast method is presented for computing the topological entropy of braids on
the torus. This work is motivated by the need to analyze large braids when
studying two-dimensional flows via the braiding of a large number of particle
trajectories. Our approach is a generalization of Moussafir's technique for
braids on the sphere. Previous methods for computing topological entropies
include the Bestvina--Handel train-track algorithm and matrix representations
of the braid group. However, the Bestvina--Handel algorithm quickly becomes
computationally intractable for large braid words, and matrix methods give only
lower bounds, which are often poor for large braids. Our method is
computationally fast and appears to give exponential convergence towards the
exact entropy. As an illustration we apply our approach to the braiding of both
periodic and aperiodic trajectories in the sine flow. The efficiency of the
method allows us to explore how much extra information about flow entropy is
encoded in the braid as the number of trajectories becomes large.Comment: 19 pages, 44 figures. SIAM journal styl
Searching for the Physical Drivers of Eigenvector-1: From Quasars to Nano-Quasars
We point out an analogy between two accreting white dwarfs with jets (CH Cyg
and MWC 560) and powerful quasars. In spite of the enormous difference in the
mass of the central object (a factor about 10^7), the emission lines are
strikingly similar to those of I Zw1 (the prototype "Narrow Line Seyfert 1"
nucleus whose spectrum is widely used as an FeII template for almost all
quasars). The spectral similarity give us the unique possibility to consider
the optical Eigenvector-1 diagram using objects less massive by a factor of
millions. Our results reinforce the interpretation of the "Eigenvector-1
correlations" found for low redshift quasars as driven mainly by the source
luminosity to central compact object mass ratio(L/M). The accreting white
dwarfs CH Cyg and MWC 560, their jets and emission lines, may well represent
the low energy, non relativistic end of the accretion phenomena, which
encompass the most powerful quasars and the microquasars. The remarkable
similarities suggest that they may be legitimately considered "nano-quasars".Comment: 5 pages, 2 figures, accepted by the Astrophysical Journal (Letters
Parallel Unsmoothed Aggregation Algebraic Multigrid Algorithms on GPUs
We design and implement a parallel algebraic multigrid method for isotropic
graph Laplacian problems on multicore Graphical Processing Units (GPUs). The
proposed AMG method is based on the aggregation framework. The setup phase of
the algorithm uses a parallel maximal independent set algorithm in forming
aggregates and the resulting coarse level hierarchy is then used in a K-cycle
iteration solve phase with a -Jacobi smoother. Numerical tests of a
parallel implementation of the method for graphics processors are presented to
demonstrate its effectiveness.Comment: 18 pages, 3 figure
Early perioperative res ults in 53 cases of locally rec urrent colorectal cancer
Purpose: The objective of this study was to analyze retrospectively the early perioperative results in a cohort of 53 patients with localy reccurent colorectal cancer (CRC).Material and methods: The study covered 53 patients with CRC 21 males and 32 females at a mean age of 62 years treated in the Clinic of Liver, Biliary, Pancreatic and General Surgery, Tokuda Hospital of Sofia, during the period from January 2007 to March 2013. Any necessary diagnostic and surgical methods were applied.Results: The locally recurrent CRC is a challenge for the surgeon because of the fact that in most cases it engages adjacent anatomical structures and organs, on the one hand, and it is accompanied by complications, on the other hand.Conclusion: Achievement of good late results in patients with recurrent CRC is due to radicality of the interventions. Most often, they should be multivisceral resections. The presence of intestinal obstruction of varying degree and of synchronous peritoneal and liver metastases commonly limit the possibilities for surgical interference with the disease. Particular attention should be paid to possible neoadjuvant treatment capable of reducing the stage of diasease and improving the perioperative outcomes. Therapeutic behaviour should be strictly individual and consider any possible options. The experience of the surgical team is extremely important, too
Locally advanced adenocarcinoma of the supramesocolic part of the colon . Feat ures of surgical treatment and challenges
Purpose: The objective of the present study was to analyze the early results from the surgical treatment of locally advanced carcinoma of the colon in its transverse section and the two flexures.Material and methods: The study covered 36 patients with locally advanced colonic carcinoma, 19 males and 17 females at a mean age of 65,6 years, treated in the Clinic of Liver, Biliary, Pancreatic and General Surgery, Tokuda Hospital of Sofia during the period from January 2007 to March 2013. Any necessary diagnostic and surgical methods were applied.Results: Multivisceral resections were commonly performed in order to achieve a radical surgery in cases of locally advanced disease. Great surgeon`s experience in liver, biliary and pancreatic interventions is obligatorily required. In this paper we share our experience in the treatment of this disease for a period of 6 years.Conclusion: Our application of the multivisceral resections results in surgical radicality along with acceptable levels of perioperative morbidity and mortality rates when compared to other studies in in the foreign literature available
Multivisceral ‘en-bloc` resections of colorectal tumours - milestones in the surgical techniques
Purpose: Colorectal tumours (CRT) consisting mainly of colorectal cancer (CRC) are diagnosed sometimes at an advanced T4 stage, i. e. local involvement of neighbouring organ/organs and anatomical structure/ structures. Aggressive surgical approach preceded and/or followed by neo-adjuvant/adjuvant therapy is advocated because of proven benefit for the patient. The aim of this study was to carry out a literature survey, on the one hand, and to analyze the cases from the authors` institutional experience, on the other hand, in an attempt to submit for consideration the milestones of the multivisceral en-block resections in cases of locally advanced CRTs, i.e. to describe the specific surgical approaches depending on different tumour location and peritumoural involvement of adjacent structures and organs.Material and methods: A retrospective analysis of 154 cases of CRT was performed, all of them operated in the Clinic of Liver, Biliary, Pancreatic and General Surgery, Tokuda Hospital of Sofia, from January 1, 2007 to March 31, 2013. All the patients were diagnosed in an advanced T4-stage and received multivisceral en-bloc resections. Three main groups of methods that had been used were analyzed: 1) preoperative diagnosis, giving a hint of multivisceral en-bloc resection; 2) intraoperative assessment - gross tumour appearance, frozen sections (?), final histological examinations, and 3) surgical methods.Results: Early morbidity and mortality rates were 22,6% and 5,8%, respectively, without any significant difference when compared with ‘simple` colon and rectum resections and with literature data available.Conclusion: Multivisceral en-bloc resection for CRCs has been performed in more than 10% of the cases. It benefits the long-term prognosis. Tumour location and number of resected organs are essential characteristics of these procedures and they are independently associated with the quantity of intraoperative blood loss, higher early morbidity rates and more frequent local recurrence
Upper limits for a narrow resonance in the reaction p + p -> K^+ + (Lambda p)
The reaction pp -> K^+ + (Lambda p) has been measured at T_p = 1.953 GeV and
\Theta = 0 deg with a high missing mass resolution in order to study the Lambda
p final state interaction. Narrow S = -1 resonances predicted by bag model
calculations are not visible in the missing mass spectrum. Small structures
observed in a previous experiment are not confirmed. Upper limits for the
production cross section of a narrow resonance are deduced for missing masses
between 2058 and 2105 MeV/c^2.Comment: 8 pages, 5 figure
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