Perturbative Analysis of Spectral Singularities and Their Optical Realizations

We develop a perturbative method of computing spectral singularities of a Schreodinger operator defined by a general complex potential that vanishes outside a closed interval. These can be realized as zero-width resonances in optical gain media and correspond to a lasing effect that occurs at the threshold gain. Their time-reversed copies yield coherent perfect absorption of light that is also known as an antilaser. We use our general results to establish the exactness of the n-th order perturbation theory for an arbitrary complex potential consisting of n delta-functions, obtain an exact expression for the transfer matrix of these potentials, and examine spectral singularities of complex barrier potentials of arbitrary shape. In the context of optical spectral singularities, these correspond to inhomogeneous gain media.Comment: 13 pages, 2 figures, one table, a reference added, typos correcte

Supersymmetric Effects on Isospin Symmetry Breaking and Direct CP Violation in B→ργB \to \rho \gamma

We argue that one can search for physics beyond the standard model through measurements of the isospin-violating quantity $\Delta^{-0} \equiv \Gamma(B^- \to \rho^- \gamma)/2\Gamma(B^0 \to \rho^0 \gamma)-1$, its charge conjugate $\Delta^{+0}$, and direct CP violation in the partial decay rates of $B^\pm \to \rho^\pm \gamma$. We illustrate this by working out theoretical profiles of the charge-conjugate averaged ratio $\Delta \equiv {1 \over 2}(\Delta^{+0} +\Delta^{-0})$ and the CP asymmetry $A_{CP}(B^\pm \to \rho^\pm \gamma)$ in the standard model and in some variants of the minimal supersymmetric standard model. We find that chargino contributions in the large $\tan \beta$ region may modify the magnitudes and flip the signs of $\Delta$ and $A_{CP}(B^\pm \to \rho^\pm \gamma)$ compared to their standard-model values, providing an unmistakeable signature of supersymmetry.Comment: 10 pages, 7 figures (requires graphicx

Isospin Considerations in Correlations of Pions and BB mesons

The correlations between a $B$ meson and a pion produced nearby in phase space should respect isospin reflection symmetry $I_3 \to -I_3$. Thus, one generally expects similar $\pi^+ B^0$ and $\pi^- B^+$ correlations (non-exotic channels), and similar $\pi^- B^0$ and $\pi^+ B^+$ correlations (exotic channels). Exceptions include (a) fragmentation processes involving exchange of quarks with the producing system, (b) misidentification of charged kaons as charged pions, and (c) effects of decay products of the associated $\overline{B}$. All of these can affect the apparent signal for correlations of charged $B$ mesons with charged hadrons. The identification of the flavor of neutral $B$ mesons through the decay $B^0 \to K^{*0} J/\psi$ requires good particle identification in order that the decay $K^{*0} \to K^+ \pi^-$ not be mistaken for $\overline{K}^{*0} \to K^- \pi^+$, in which case the correlations of neutral $B$ mesons with hadrons can be underestimated.Comment: LaTeX EPSF file; 8 uuencoded figures to be submitted separatel

Multiple classical limits in relativistic and nonrelativistic quantum mechanics

The existence of a classical limit describing interacting particles in a second-quantized theory of identical particles with bosonic symmetry is proved. This limit exists in addition to a previously established classical limit with a classical field behavior, showing that the limit $\hbar \to 0$ of the theory is not unique. An analogous result is valid for a free massive scalar field: two distinct classical limits are proved to exist, describing a system of particles or a classical field. The introduction of local operators in order to represent kinematical properties of interest is shown to break the permutation symmetry under some localizability conditions, allowing the study of individual particle properties.Comment: 13 page

Specific recognition of a multiply phosphorylated motif in the DNA repair scaffold XRCC1 by the FHA domain of human PNK.

Short-patch repair of DNA single-strand breaks and gaps (SSB) is coordinated by XRCC1, a scaffold protein that recruits the DNA polymerase and DNA ligase required for filling and sealing the damaged strand. XRCC1 can also recruit end-processing enzymes, such as PNK (polynucleotide kinase 3'-phosphatase), Aprataxin and APLF (aprataxin/PNK-like factor), which ensure the availability of a free 3'-hydroxyl on one side of the gap, and a 5'-phosphate group on the other, for the polymerase and ligase reactions respectively. PNK binds to a phosphorylated segment of XRCC1 (between its two C-terminal BRCT domains) via its Forkhead-associated (FHA) domain. We show here, contrary to previous studies, that the FHA domain of PNK binds specifically, and with high affinity to a multiply phosphorylated motif in XRCC1 containing a pSer-pThr dipeptide, and forms a 2:1 PNK:XRCC1 complex. The high-resolution crystal structure of a PNK-FHA-XRCC1 phosphopeptide complex reveals the basis for this unusual bis-phosphopeptide recognition, which is probably a common feature of the known XRCC1-associating end-processing enzymes

Revisiting the double-binary-pulsar probe of non-dynamical Chern-Simons gravity

One of the popular modifications to the theory of general relativity is non-dynamical Chern-Simons (CS) gravity, in which the metric is coupled to an externally prescribed scalar field. Setting accurate constraints to the parameters of the theory is important owing to their implications for the scalar field and/or the underlying fundamental theory. The current best constraints rely on measurements of the periastron precession rate in the double-binary-pulsar system and place a very tight bound on the characteristic CS lengthscale k_cs^{-1} <~ 3*10^{-9} km. This paper considers several effects that were not accounted for when deriving this bound and lead to a substantial suppression of the predicted rate of periastron precession. It is shown, in particular, that the point mass approximation for extended test bodies does not apply in this case. The constraint to the characteristic CS lengthscale is revised to k_cs^{-1} <~ 0.4 km, eight orders of magnitude weaker than what was previously found.Comment: 12 pages, 4 figures, to be submitted to PRD. Comments are welcom

Using historical lesion volume data in the design of a new phase II clinical trial in acute stroke

&lt;p&gt;&lt;b&gt;Background and Purpose:&lt;/b&gt; Clinical research into the treatment of acute stroke is complicated, is costly, and has often been unsuccessful. Developments in imaging technology based on computed tomography and magnetic resonance imaging scans offer opportunities for screening experimental therapies during phase II testing so as to deliver only the most promising interventions to phase III. We discuss the design and the appropriate sample size for phase II studies in stroke based on lesion volume.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Methods:&lt;/b&gt; Determination of the relation between analyses of lesion volumes and of neurologic outcomes is illustrated using data from placebo trial patients from the Virtual International Stroke Trials Archive. The size of an effect on lesion volume that would lead to a clinically relevant treatment effect in terms of a measure, such as modified Rankin score (mRS), is found. The sample size to detect that magnitude of effect on lesion volume is then calculated. Simulation is used to evaluate different criteria for proceeding from phase II to phase III.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Results:&lt;/b&gt; The odds ratios for mRS correspond roughly to the square root of odds ratios for lesion volume, implying that for equivalent power specifications, sample sizes based on lesion volumes should be about one fourth of those based on mRS. Relaxation of power requirements, appropriate for phase II, lead to further sample size reductions. For example, a phase III trial comparing a novel treatment with placebo with a total sample size of 1518 patients might be motivated from a phase II trial of 126 patients comparing the same 2 treatment arms.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Discussion:&lt;/b&gt; Definitive phase III trials in stroke should aim to demonstrate significant effects of treatment on clinical outcomes. However, more direct outcomes such as lesion volume can be useful in phase II for determining whether such phase III trials should be undertaken in the first place.&lt;/p&gt

Screening of Guava genotypes to natural infestation of fruit flies (Diptera:Tephritidae) in River Nile, Sennar and North Kordofan States, Sudan

The infesting species and their infestation indices of fruit flies were determined for guava genotypes (Psidium guajava L.),grown in River Nile, Sennar and North Kordofan States during the period from June to August 2010 .Twenty genotypes were selected from each state to be evaluated ,where ten mature fruits from each genotypes were harvested randomly from insecticide unsprayed trees. Fruits were brought to the laboratory and placed in individual plastic vials containing sand at the bottom to obtain the pupae. Infestation indices were estimated by means of total number of pupae/fruit. Pupal viability was then calculated based on the percentage of pupae resulted in fly emergence. Data was analyzed using analysis of variance and Duncan multiple range test for mean separations. Results showed that Guava fruits were infested by four fruit fly species Ceratitis cosyra, C.quinaira, C capitata and Bactrocera dorsalis constitute (82.2), (0.8), (16.7), (0.3% ) and 28.35 ,0.01 ,10.1 and 61.56% in River Nile and Sennar States respectively. While in North Kordofan State guava fruits were infested by C.cosyra, C.capitat and B.dorsalis 98.4,0.4 and 1.2% respectively. All the evaluated genotypes in River Nile and Sennar States were infested by the fruit fly with varying degrees only two genotypes 15 red flesh fruit and 19 white flesh fruit in Kordofan state were found free from fruit fly infestation. Infestation was much higher in Sennar and River Nile states (32 and 29 pupae/fruit) respectively compared to North Kordofan (1.6 pupae/fruit).The higher infestation rate occurred in ripe guava fruits (33) compared to 18 and 6 pupae/fruit in mature green and immature green fruit respectively