Ratio of Λˉ/Λ\bar{\Lambda}/\Lambda in Semi-inclusive Electroproduction

It is shown that the $\bar{\Lambda}/\Lambda$ cross section ratio in semi-inclusive electroproduction of $\Lambda$ and $\bar{\Lambda}$ hyperons in deep inelastic scattering of charged lepton on a nucleon target, can provide useful information on the quark to $\Lambda$ fragmentation functions. This ratio is calculated explicitly in a quark-diquark model, a pQCD based analysis, and an SU(3) symmetry model, with three different options for the contribution from the unfavored fragmentation functions. The $x$-dependence of this ratio is sensitive to the ratio of unfavored fragmentation functions over favored fragmentation functions, $D_{\bar{u}}^{\Lambda}(z)/D_{u}^{\Lambda}(z)$, whereas the $z$-dependence is sensitive to the flavor structure of the fragmentation functions, i.e., the ratio $D_u^{\Lambda}(z)/D_s^{\Lambda}(z)$. Future measurements by the HERMES Collaboration at DESY can discriminate between various cases.Comment: 11 latex files, 6 figure

Particle-Antiparticle Asymmetries of Λ\Lambda Production in Hadron-Nucleon Collisions

The particle-antiparticle asymmetries of $\Lambda$ production in 250 GeV/c $\pi^{\pm}$, $K^{\pm}$, and $p$ --nucleon collisions are studied with two model parametrizations of quark to $\Lambda$ fragmentation functions. It is shown that the available data can be qualitatively explained by the calculated results in both the quark-diquark model and a pQCD based analysis of fragmentation functions. The differences in the two model predictions are significant for $K^{\pm}$ beams, and high precision measurements of the asymmetries with detailed $x_F$ and $P_T$ information can discriminate between different predictions.Comment: 14 LaTex pages, 4 figures, to appear in Phys. Lett.

Flavor and Spin Structure of Λ\Lambda-Baryon at Large x

It is shown that a perturbative QCD (pQCD) based analysis and the SU(6) quark-diquark model give significant different predictions concerning the flavor and spin structure for the quark distributions of the $\Lambda$-baryon near $x=1$. Detailed predictions for the ratios $u(x)/s(x)$ of unpolarized quark distributions, $\Delta s(x)/s(x)$ of valence strange quark, and $\Delta u(x)/u(x)$ of valence up and down quarks of the $\Lambda$ are given from the quark-diquark model and from a pQCD based model. It is found that the up and down quarks are positively polarized at large $x$, even though their net spin contributions to the $\Lambda$ might be zero or negative. The significant difference for $u(x)/s(x)$ between the two different approaches are predicted. The prediction of positively polarized up and down quarks inside the $\Lambda$ at large $x$ has been supported by the available data of $\Lambda$-polarization in $Z$ decays and also by the most recent HERMES result of spin transfer to the $\Lambda$ in deep elastic scattering of polarized lepton on the nucleon target.Comment: 13 latex pages, one figure added, three eps figures, abstract and discussions changed, prediction comparison with new experimental data added, version to appear in PL

Flavor and Spin Structure of Octet Baryons at Large x

The quark flavor and spin distributions in octet baryons are calculated both in the SU(6) quark spectator diquark model and in a perturbative QCD (pQCD) based model. It is shown that the $\Lambda$ has the most significant difference in flavor structure at large $x$ between the two models, though the flavor and spin structure of other baryons can also provide tests of different models. The Drell-Yan process for $\Sigma^{\pm}$ beams on isoscalar targets can be used to test different predictions concerning the valence quark flavor structure of the $\Sigma^{\pm}$.Comment: 24 pages, 11 figures, version published in Nucl.Phys.B 574 (2000) 33

Recalculation of Pion Compton Scattering in Perturbative QCD

We recalculated pion virtual Compton scattering in perturbative QCD in this paper. Our calculation avoids some deficiencies in existing literatures, and treats real Compton scattering as a limit case in which the mass of the virtual photon equals to zero. Expressions of the hard scattering amplitudes from 10 independent diagrams are given explicitly in the text. By comparing the effects of different distribution amplitudes on physical observables, we studied the self-consistence of pQCD calculation of this problem.Comment: 15 pages, 8 eps figs. accepted by Phys. Lett

Pharmacogenomics and cancer stem cells: a changing landscape?

Pharmacogenomics in oncology holds the promise to personalize cancer therapy. However, its clinical application is still limited to a few genes, and, in the large majority of cancers, the correlation between genotype and clinical outcome has been disappointing. One possible explanation is that current pharmacogenomic studies do not take into account the emerging role of cancer stem cells (CSCs) in drug sensitivity and resistance. CSCs are a subpopulation of cells driven by specific signal-transduction pathways, but genetic variants affecting their activity are generally neglected in current pharmacogenomic studies. Moreover, in several malignancies, CSCs represent a rare sub-population; therefore, whole tumor profiling might mask CSC gene expression patterns. This article reviews current evidence on CSC chemoresistance and shows how common genetic variations in CSC-related genes may predict individual response to anti-cancer agents. Furthermore, we provide insights into the design of pharmacogenomic studies to address the clinical usefulness of CSC genetic profiling

Applicability of Perturbative QCD to Pion Virtual Compton Scattering

We study explicitly the applicability of perturbative QCD (pQCD) to the pion virtual Compton scattering. It is found that there are central-region singularities introduced by the QCD running coupling constant, in addition to the end-point singularities generally existed in other exclusive processes such as the pion form factor. We introduce a simple technique to evaluate the contributions from these singularities, so that we can arrive at a judgement that these contributions will be unharmful to the applicability of pQCD at certain energy scale, i.e., the ``work point'' which is defined to determine when pQCD is applicable to exclusive processes. The applicability of pQCD for different pion distribution amplitudes are explored in detail. We show that pQCD begins to work at 10 ${GeV}^2$. If we relax our constraint to a weak sense, the work point may be as low as 4 ${GeV}^2$.Comment: 13 Latex pages, 10 figures, to appear in PL

Economic Evaluation of Newborn Screening for Severe Combined Immunodeficiency

Evidence on the cost-effectiveness of newborn screening (NBS) for severe combined immunodeficiency (SCID) in the Australian policy context is lacking. In this study, a pilot population-based screening program in Australia was used to model the cost-effectiveness of NBS for SCID from the government perspective. Markov cohort simulations were nested within a decision analytic model to compare the costs and quality-adjusted life-years (QALYs) over a time horizon of 5 and 60 years for two strategies: (1) NBS for SCID and treat with early hematopoietic stem cell transplantation (HSCT); (2) no NBS for SCID and treat with late HSCT. Incremental costs were compared to incremental QALYs to calculate the incremental cost-effectiveness ratios (ICER). Sensitivity analyses were performed to assess the model uncertainty and identify key parameters impacting on the ICER. In the long-term over 60 years, universal NBS for SCID would gain 10 QALYs at a cost of US $0.3 million, resulting in an ICER of US$33,600/QALY. Probabilistic sensitivity analysis showed that more than half of the simulated ICERs were considered cost-effective against the common willingness-to-pay threshold of A$50,000/QALY (US$35,000/QALY). In the Australian context, screening for SCID should be introduced into the current NBS program from both clinical and economic perspectives

Cosmic microwave background and large scale structure limits on the interaction between dark matter and baryons

We study the effect on the cosmic microwave background (CMB) anisotropy and large scale structure (LSS) power spectrum of a scattering interaction between cold dark matter and baryons. This scattering alters the CMB anisotropy and LSS spectrum through momentum transfer between the cold dark matter particles and the baryons. We find that current CMB observations can put an upper limit on the scattering cross section which is comparable with or slightly stronger than previous disk heating constraints at masses greater than 1 GeV, and much stronger at smaller masses. When large-scale structure constraints are added to the CMB limits, our constraint is more stringent than this previous limit at all masses. In particular, a dark matter-baryon scattering cross section comparable to the ``Spergel-Steinhardt'' cross section is ruled out for dark matter mass greater than 1 GeV.Comment: 8 pages, 2 figures, use RevTeX4, submitted to PRD replaced with revised versio