Group a streptococcal serotypes isolated from healthy schoolchildren in iran

Serotypes of group A streptococci are still a major cause of pharyngitis and some post-infectious sequelae such as rheumatic fever. As part of the worldwide effort to clarify the epidemiological pattern of group A streptococci in different countries, the present study was conducted to assess the prevalence of Streptococcus pyogenes serotypes in Iran. A total of 1588 throat swabs were taken from healthy school children in the city of Gorgan during February and March 1999. Of those isolates, 175 resulted positive for group A streptococci. The distribution pattern was similar for girls and boys, with 10.8 and 11.2, respectively. Urban school children showed a higher rate of colonization compared to those in rural areas. Serotyping was performed on 65 of the positive isolates using standard techniques, and only 21 (32) were M-type isolates. Their profiles fell into four types with M1 predominating, which could reflect the presence of rheumatic fever in the region. However, when isolates were challenged for T-antigen types, nearly all were positive (94). The pattern of T types was diverse (18 types), with the most common T types being T1 (26), TB3264 (15), TB\1-19 & B\25\1-19 (9.2) and T2 & 2\28 (7.7). When isolates were tested for opacity factor, only 23 (35) were positive while 34 (52) responded to the serum opacity reaction test. Although the number of isolates in this study was not sufficient to make any epidemiological conclusions, the scarcity of serotyping studies in Iran could render these data useful for future attempts to develop a streptococcal vaccine

A classical model for the negative dc conductivity of ac-driven 2D electrons near the cyclotron resonance

A classical model for {\em dc} transport of two dimensional electrons in a perpendicular magnetic field and under strong irradiation is considered. We demonstrate that, near the cyclotron resonance condition, and for {\em linear} polarization of the {\em ac} field, a strong change of the diagonal component, $\sigma_d$, of the {\em dc} conductivity occurs in the presence of a {\em weak} nonparabolicity of the electron spectrum. Small change in the electron effective mass due to irradiation can lead to negative $\sigma_d$, while the Hall component of the {\em dc} conductivity remains practically unchanged. Within the model considered, the sign of $\sigma_d$ depends on the relative orientation of the {\em dc} and {\em ac} fields, the sign of the detuning of the {\em ac} frequency from the cyclotron resonance, and the sign of nonparabolic term in the energy spectrum.Comment: 4 pages, 1 figur

Periodic orbit effects on conductance peak heights in a chaotic quantum dot

We study the effects of short-time classical dynamics on the distribution of Coulomb blockade peak heights in a chaotic quantum dot. The location of one or both leads relative to the short unstable orbits, as well as relative to the symmetry lines, can have large effects on the moments and on the head and tail of the conductance distribution. We study these effects analytically as a function of the stability exponent of the orbits involved, and also numerically using the stadium billiard as a model. The predicted behavior is robust, depending only on the short-time behavior of the many-body quantum system, and consequently insensitive to moderate-sized perturbations.Comment: 14 pages, including 6 figure

The path-coalescence transition and its applications

We analyse the motion of a system of particles subjected a random force fluctuating in both space and time, and experiencing viscous damping. When the damping exceeds a certain threshold, the system undergoes a phase transition: the particle trajectories coalesce. We analyse this transition by mapping it to a Kramers problem which we solve exactly. In the limit of weak random force we characterise the dynamics by computing the rate at which caustics are crossed, and the statistics of the particle density in the coalescing phase. Last but not least we describe possible realisations of the effect, ranging from trajectories of raindrops on glass surfaces to animal migration patterns.Comment: 4 pages, 3 figures; revised version, as publishe

Baryon masses at second order in large-NN chiral perturbation theory

We consider flavor breaking in the the octet and decuplet baryon masses at second order in large-$N$ chiral perturbation theory, where $N$ is the number of QCD colors. We assume that $1/N \sim 1/N_F \sim m_s / \Lambda \gg m_{u,d}/\Lambda, \alpha_{EM}$, where $N_F$ is the number of light quark flavors, and $m_{u,d,s} / \Lambda$ are the parameters controlling $SU(N_F)$ flavor breaking in chiral perturbation theory. We consistently include non-analytic contributions to the baryon masses at orders $m_q^{3/2}$, $m_q^2 \ln m_q$, and $(m_q \ln m_q) / N$. The $m_q^{3/2}$ corrections are small for the relations that follow from $SU(N_F)$ symmetry alone, but the corrections to the large-$N$ relations are large and have the wrong sign. Chiral power-counting and large-$N$ consistency allow a 2-loop contribution at order $m_q^2 \ln m_q$, and a non-trivial explicit calculation is required to show that this contribution vanishes. At second order in the expansion, there are eight relations that are non-trivial consequences of the $1/N$ expansion, all of which are well satisfied within the experimental errors. The average deviation at this order is 7 \MeV for the \De I = 0 mass differences and 0.35 \MeV for the \De I \ne 0 mass differences, consistent with the expectation that the error is of order $1/N^2 \sim 10\%$.Comment: 19 pages, 2 uuencoded ps figs, uses revte

Brane World Susy Breaking from String/M Theory

String and M-theory realizations of brane world supersymmetry breaking scenarios are considered in which visible sector Standard Model fields are confined on a brane, with hidden sector supersymmetry breaking isolated on a distant brane. In calculable examples with an internal manifold of any volume the Kahler potential generically contains brane--brane non-derivative contact interactions coupling the visible and hidden sectors and is not of the no-scale sequestered form. This leads to non-universal scalar masses and without additional assumptions about flavor symmetries may in general induce dangerous sflavor violation even though the Standard Model and supersymmetry branes are physically separated. Deviations from the sequestered form are dictated by bulk supersymmetry and can in most cases be understood as arising from exchange of bulk supergravity fields between branes or warping of the internal geometry. Unacceptable visible sector tree-level tachyons arise in many models but may be avoided in certain classes of compactifications. Anomaly mediated and gaugino mediated contributions to scalar masses are sub-dominant except in special circumstances such as a flat or AdS pure five--dimensional bulk geometry without bulk vector multiplets.Comment: Latex, 83 pages, references adde

Suppression of inhomogeneous broadening in rf spectroscopy of optically trapped atoms

We present a novel method for reducing the inhomogeneous frequency broadening in the hyperfine splitting of the ground state of optically trapped atoms. This reduction is achieved by the addition of a weak light field, spatially mode-matched with the trapping field and whose frequency is tuned in-between the two hyperfine levels. We experimentally demonstrate the new scheme with Rb 85 atoms, and report a 50-fold narrowing of the rf spectrum

Brane-induced supersymmetry breaking

We study spontaneous supersymmetry breaking induced by brane-localized dynamics in five-dimensional supergravity compactified on S^1/Z_2. We consider a model with gravity in the bulk and matter localized on tensionless branes at the orbifold fixed points. We assume that the brane dynamics give rise to effective brane superpotentials that trigger the supersymmetry breaking. We analyze in detail the super-Higgs effect. We compute the full spectrum and show that the symmetry breaking is spontaneous but nonlocal in the fifth dimension. We demonstrate that the model can be interpreted as a new, non-trivial implementation of a coordinate-dependent Scherk-Schwarz compactification.Comment: 15 pages. v2: improved treatment of brane actions, relation with conventional Scherk-Schwarz mechanism clarified, version to be published in JHE

The Magnificent Seven: Magnetic fields and surface temperature distributions

Presently seven nearby radio-quiet isolated neutron stars discovered in ROSAT data and characterized by thermal X-ray spectra are known. They exhibit very similar properties and despite intensive searches their number remained constant since 2001 which led to their name ``The Magnificent Seven''. Five of the stars exhibit pulsations in their X-ray flux with periods in the range of 3.4 s to 11.4 s. XMM-Newton observations revealed broad absorption lines in the X-ray spectra which are interpreted as cyclotron resonance absorption lines by protons or heavy ions and / or atomic transitions shifted to X-ray energies by strong magnetic fields of the order of 10^13 G. New XMM-Newton observations indicate more complex X-ray spectra with multiple absorption lines. Pulse-phase spectroscopy of the best studied pulsars RX J0720.4-3125 and RBS 1223 reveals variations in derived emission temperature and absorption line depth with pulse phase. Moreover, RX J0720.4-3125 shows long-term spectral changes which are interpreted as due to free precession of the neutron star. Modeling of the pulse profiles of RX J0720.4-3125 and RBS 1223 provides information about the surface temperature distribution of the neutron stars indicating hot polar caps which have different temperatures, different sizes and are probably not located in antipodal positions.Comment: 10 pages, 8 figures, to appear in Astrophysics and Space Science, in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface", edited by D. Page, R. Turolla and S. Zan

Strong Conformal Dynamics at the LHC and on the Lattice

Conformal technicolor is a paradigm for new physics at LHC that may solve the problems of strong electroweak symmetry breaking for quark masses and precision electroweak data. We give explicit examples of conformal technicolor theories based on a QCD-like sector. We suggest a practical method to test the conformal dynamics of these theories on the lattice.Comment: v2: Generalized discussion of lattice measurement of hadron masses, references added, minor clarifications v3: references added, minor change