452 research outputs found
Tachyon Field Quantization and Hawking Radiation
We quantize the tachyon field in a static two dimensional dilaton gravity
black hole background,and we calculate the Hawking radiation rate. We find that
the thermal radiation flux, due to the tachyon field, is larger than the
conformal matter one. We also find that massive scalar fields which do not
couple to the dilaton, do not give any contribution to the thermal radiation,
up to terms quadratic in the scalar curvature.Comment: 13 pages, Latex file, 1 figure available upon reques
Codon 89 polymorphism in the human 5 α -reductase gene in primary breast cancer
The enzyme human steroid 5-α reductase type II (SRD5A2) and androgen receptor (AR) are critical mediators of androgen action, suggesting a potential role in hormonally related cancers. The SRD5A2 gene harbours two frequent polymorphic sites, one in the coding region, at codon 89 of exon 1, where valine is substituted by leucine (V89L) and the other in the 3′ untranslated region (3′ UTR) where a variable number of dinucleotide TA repeat lengths exists. The V89L polymorphism is known to alter the activity of this enzyme. In the present study we examined 144 sporadic breast tumours from Italian patients for the V89L and TA polymorphisms by sequence and fragment analysis, respectively. Tumour extract prostate specific antigen (PSA) concentration as well as a number of well-established clinical and pathological parameters were evaluated. The results show that 53% of the tumours were homozygous for VV alleles, 37% were heterozygous for VL alleles and 10% were homozygous for LL alleles. TA(0) repeats were found in tumours with VV, LL and VL genotypes. TA(9) repeats were only found in VV homozygotes and were totally absent from either LL homozygotes or VL heterozygotes. PSA expression was significantly elevated in tumours with VV genotype. The presence of LL alleles in breast tumours is associated with earlier onset and shorter disease-free (RR = 2.65;P = 0.013) and overall survival (RR = 3.06;P = 0.014) rates. The VV genotype is associated with a more favourable prognosis. Our study suggests that the polymorphism in codon 89 of exon 1 of the human 5α-reductase gene is related with TA repeat genotypes, PSA expression and breast cancer prognosis. More specifically, we found that the LL genotype is also associated with earlier onset and more aggressive forms of breast cancer. Long-term-outcome studies are needed to investigate the relevance of this polymorphism to breast cancer susceptibility. © 2001 Cancer Research Campaign http://www.bjcancer.co
Creatine kinase BB isoenzyme levels in tumour cytosols and survival of breast cancer patients.
Creatinine kinase BB (CK-BB) is elevated in many tumours including those of the breast. We have recently described a new, highly sensitive and specific method for measuring CK-BB, based on monoclonal antibodies and time-resolved fluorometry. Using this method, we quantitated CK-BB in 172 breast tumour cytosols and examined the associations between CK-BB and other clinicopathological variables and patient survival. High CK-BB levels were seen more frequently in tumours from patients who were younger (age < 50 years), patients who qualified for chemotherapy and patients with oestrogen receptor-positive tumours. No association was seen between CK-BB and tumour stage, grade, size, histological type or the progesterone receptor. In univariate analysis, the risk of relapse or death was higher in the group with tumours containing high CK-BB levels but the difference did not reach statistical significance. In multivariate analysis, the risk of death was statistically significantly higher in the high-CK-BB group. Analysis of subsets of patients revealed that patients with oestrogen receptor-negative cancer have higher risk of death if their tumours contain high levels of CK-BB. Our data suggest that, in general, CK-BB is associated with more aggressive tumours but its value as a prognostic indicator is limited. CK-BB content of breast tumours may be more useful as an aid in selecting therapy directed at inhibiting this enzyme activity and thus depriving tumour cells of their energy source
On the Stability of the Classical Vacua in a Minimal SU(5) 5-D Supergravity Model
We consider a five-dimensional supergravity model with SU(5) gauge symmetry
and the minimal field content. Studying the arising scalar potential we find
that the gauging of the symmetry of the five-dimensional supergravity
causes instabilities. Lifting the instabilities the vacua are of Anti-de-Sitter
type and SU(5) is broken along with supersymmetry. Keeping the
ungauged the potential has flat directions along which supersymmetry is
unbroken.Comment: 24 pages, 2 figure
The issue of Dark Energy in String Theory
Recent astrophysical observations, pertaining to either high-redshift
supernovae or cosmic microwave background temperature fluctuations, as those
measured recently by the WMAP satellite, provide us with data of unprecedented
accuracy, pointing towards two (related) facts: (i) our Universe is accelerated
at present, and (ii) more than 70 % of its energy content consists of an
unknown substance, termed dark energy, which is believed responsible for its
current acceleration. Both of these facts are a challenge to String theory. In
this review I outline briefly the challenges, the problems and possible avenues
for research towards a resolution of the Dark Energy issue in string theory.Comment: Based on Invited lecture at the ``Third Aegean Summer School on: The
Invisible Universe: Dark matter and Dark energy'', Karfas, Chios Island
(Greece) September 26-October 1 200
Composite Supersymmetries in low-dimensional systems
Starting from a N=1 scalar supermultiplet in 2+1 dimensions, we demonstrate
explicitly the appearance of induced N=1 vector and scalar supermultiplets of
composite operators made out of the fundamental supersymmetric constituents. We
discuss an extension to a N=2 superalgebra with central extension, due to the
existence of topological currents in 2+1 dimensions. As a specific model we
consider a supersymmetric -model as the constituent theory, and
discuss the relevance of these results for an effective description of the
infrared dynamics of planar high-temperature superconducting condensed matter
models with quasiparticle excitations near nodal points of their Fermi surface.Comment: 20 pages Latex, no figure
- …