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Cosmos++: Relativistic Magnetohydrodynamics on Unstructured Grids with Local Adaptive Refinement (open access)

Cosmos++: Relativistic Magnetohydrodynamics on Unstructured Grids with Local Adaptive Refinement

A new code and methodology are introduced for solving the fully general relativistic magnetohydrodynamic (GRMHD) equations using time-explicit, finite-volume discretization. The code has options for solving the GRMHD equations using traditional artificial-viscosity (AV) or non-oscillatory central difference (NOCD) methods, or a new extended AV (eAV) scheme using artificial-viscosity together with a dual energy-flux-conserving formulation. The dual energy approach allows for accurate modeling of highly relativistic flows at boost factors well beyond what has been achieved to date by standard artificial viscosity methods. it provides the benefit of Godunov methods in capturing high Lorentz boosted flows but without complicated Riemann solvers, and the advantages of traditional artificial viscosity methods in their speed and flexibility. Additionally, the GRMHD equations are solved on an unstructured grid that supports local adaptive mesh refinement using a fully threated oct-tree (in three dimensions) network to traverse the grid hierarchy across levels and immediate neighbors. A number of tests are presented to demonstrate robustness of the numerical algorithms and adaptive mesh framework over a wide spectrum of problems, boosts, and astrophysical applications, including relativistic shock tubes, shock collisions, magnetosonic shocks, Alfven wave propagation, blast waves, magnetized Bondi flow, and the magneto-rotational instability in Kerr black hole spacetimes.
Date: May 6, 2005
Creator: Anninos, P; Fragile, P C & Salmonson, J D
System: The UNT Digital Library
Measurement of CP Asymmetries for the Decays B^+/- --> D^0_CP K*^+/- (open access)

Measurement of CP Asymmetries for the Decays B^+/- --> D^0_CP K*^+/-

Using a sample of 232 million {Upsilon}(4S) {yields} B{bar B} events collected with the BABAR detector at the PEP-II B Factory in 1999-2004, they study B{sup -} {yields} K{sup 0}K*(892){sup -} decays where K*{sup -} {yields} K{sub S}{sup 0} {pi}{sup -} and D{sup 0} {yields} K{sup -}{pi}{sup +}, K{sup -}{pi}{sup +}{pi}{sup 0}, K{sup -}{pi}{sup +}{pi}{sup +}{pi}{sup -} (non-CP final states); K{sup +}K{sup -}, {pi}{sup +}{pi}{sup -} (CP+ eigenstates); K{sub S}{sup 0}{pi}{sup 0}, K{sub S}{sup 0}{phi} and K{sub S}{sup 0}{omega} (CP- eigenstates). They measure four observables that are sensitive to the angle {gamma} of the CKM unitarity triangle; the partial-rate charge asymmetries A{sub CP{+-}} and the ratios of the B-decay branching fraction in CP{+-} and non-CP decays R{sub CP{+-}}: A{sub CP+} = -0.08 {+-} 0.19 (stat.) {+-} 0.08 (syst.); A{sub CP-} = -0.26 {+-} 0.40 (stat.) {+-} 0.12 (syst.); R{sub CP+} = 1.96 {+-} 0.40 (stat.) {+-} 0.11 (syst.); R{sub CP-} = 0.65 {+-} 0.26 (stat.) {+-} 0.08 (syst.).
Date: July 6, 2005
Creator: Aubert, B.; Barate, R.; Boutigny, D.; Couderc, F.; Karyotakis, Y.; Lees, J. P. et al.
System: The UNT Digital Library
Measurement of the $B^+\rightarrow p \bar{p} K^{+}$ Branching Fraction and Study of the Decay Dynamics (open access)

Measurement of the $B^+\rightarrow p \bar{p} K^{+}$ Branching Fraction and Study of the Decay Dynamics

With a sample of 232 x 10{sup 6} {Upsilon}(4S) {yields} B{bar B} events collected with the BABAR detector, we study the decay B{sup +} {yields} p{bar p}K{sup +} excluding charmonium decays to p{bar p}. We measure a branching fraction {Beta}(B{sup +} {yields} p{bar p}K{sup +}) = (6.7 {+-} 0.5 {+-} 0.4) x 10{sup -6}. An enhancement at low p{bar p} mass is observed and the Dalitz plot asymmetry suggests dominance of the penguin amplitude in this B decay. We search for a pentaquark candidate {Theta}*{sup ++} decaying into pK{sup +} in the mass range 1.43 to 2.00 GeV/c{sup 2} and set limits on {Beta}(B{sup +} {yields} {Theta}*{sup ++} {bar p}) x {Beta}({Theta}*{sup ++} {yields} pK{sup +}) at the 10{sup -7} level.
Date: July 6, 2005
Creator: Aubert, B.; Barate, R.; Boutigny, D.; Couderc, F.; Karyotakis, Y.; Lees, J. P. et al.
System: The UNT Digital Library
Measurement of the Partial Branching Fraction for Inclusive Charmless Semileptonic B Decays and Extraction of |Vub| (open access)

Measurement of the Partial Branching Fraction for Inclusive Charmless Semileptonic B Decays and Extraction of |Vub|

Charmless semileptonic decays, {bar B} {yields} X{sub u}{ell}{bar {nu}}, are studied in a sample of 232 million B{bar B} decays recorded with the BABAR detector, in events where the decay of the second B meson is fully reconstructed. Inclusive charmless decays are selected in kinematic regions where the dominant background from semileptonic B decays to charm is reduced by requirements on the hadronic mass M{sub X} and the momentum transfer q{sup 2}. The partial branching fraction for {bar B} {yields} X{sub u}{ell}{bar {nu}} decays for M{sub X} < 1.7 GeV/c{sup 2} and q{sup 2} > 8 GeV{sup 2}/c{sup 4} is measured to be {Delta}{Beta}({bar b} {yields} X{sub u}{ell}{bar {nu}}) = (0.87 {+-} 0.09{sub stat} {+-} 0.09{sub sys} {+-} 0.01{sub th}) x 10{sup -3}. The CKM matrix element|V{sub ub}| is determined by using theoretical calculations of phase space acceptances. Theoretical uncertainties in this extrapolation are reduced by using the inclusive b {yields} s{gamma} photon spectrum and moments of the b {yields} c{ell}{bar {nu}} lepton energy and hadronic invariant mass.
Date: July 6, 2005
Creator: Aubert, B.; Barate, R.; Boutigny, D.; Couderc, F.; Karyotakis, Y.; Lees, J. P. et al.
System: The UNT Digital Library
Measurement of Time-Dependent CP Asymmetries and the CP-Odd Fraction in the Decay B0->D*+D*- (open access)

Measurement of Time-Dependent CP Asymmetries and the CP-Odd Fraction in the Decay B0->D*+D*-

We present an updated measurement of time-dependent CP asymmetries and the CP-odd fraction in the decay B{sup 0} D*{sup +}D*{sup -} using 232 x 10{sup 6} B{bar B} pairs collected by the BABAR detector at the PEP-II B factory. We determine the CP-odd fraction to be 0.125 {+-} 0.044(stat) {+-} 0.007(syst). The time-dependent CP asymmetry parameters C{sub +} and S{sub +} are determined to be 0.06 {+-} 0.17(stat) {+-} 0.03(syst) and -0.75 {+-} 0.25(stat) {+-} 0.03(syst), respectively. The Standard Model predicts these parameters to be 0 and -sin2{beta}, respectively, in the absence of penguin amplitude contributions.
Date: July 6, 2005
Creator: Aubert, B.; Barate, R.; Boutigny, D.; Couderc, F.; Karyotakis, Y.; Lees, J. P. et al.
System: The UNT Digital Library
Measurements of the Rare Decays B -> Kl+l- and B ->K*l+l- (open access)

Measurements of the Rare Decays B -> Kl+l- and B ->K*l+l-

The authors present measurements of the flavor-changing neutral current decays B {yields} K{ell}{sup +}{ell}{sup -} and B {yields} K*{ell}{sup +}{ell}{sup -}, where {ell}{sup +}{ell}{sup -} is either an e{sup +}e{sup -} or {mu}{sup +}{mu}{sup -} pair. The data sample comprises 229 x 10{sup 6} {Upsilon}(4S) {yields} B{bar B} decays collected with the BABAR detector at the PEP-II e{sup +}e{sup -} storage ring.
Date: July 6, 2005
Creator: Aubert, B.; Barate, R.; Boutigny, D.; Couderc, F.; Karyotakis, Y.; Lees, J. P. et al.
System: The UNT Digital Library
Observation of a Broad Structure in the $\pi^+\pi^-J/\psi$ Mass Spectrum around 4.26~GeV/$c^2$ (open access)

Observation of a Broad Structure in the $\pi^+\pi^-J/\psi$ Mass Spectrum around 4.26~GeV/$c^2$

The authors study initial-state radiation events, e{sup +}e{sup -} {yields} {gamma}{sub ISR} {pi}{sup +}{pi}{sup -} J/{psi}, with data collected with the BABAR detector. They observe an accumulation of events near 4.26 GeV/c{sup 2} in the invariant-mass spectrum of {pi}{sup +}{pi}{sup -} J/{psi}. Fits of the mass spectrum indicate that a broad resonance with a mass of about 4.26 GeV/c{sup 2} is required to describe the observed structure. The presence of additional narrow resonances cannot be excluded. The fitted width of the broad resonance is 50 to 90 MeV/c{sup 2}, depending on the fit hypothesis.
Date: July 6, 2005
Creator: Aubert, B.; Barate, R.; Boutigny, D.; Couderc, F.; Karyotakis, Y.; Lees, J. P. et al.
System: The UNT Digital Library
A Precision Measurement of the Lambda_c Baryon Mass (open access)

A Precision Measurement of the Lambda_c Baryon Mass

The {Lambda}{sub c}{sup +} baryon mass is measured using {Lambda}{sub c}{sup +} {yields} {Lambda}K{sub S}{sup 0}K{sup +} and {Lambda}{sub c}{sup +} {yields} {Sigma}{sup 0}K{sub S}{sup 0}K{sup +} decays reconstructed in 232 fb{sup -1} of data collected with the BABAR detector at the PEP-II asymmetric-energy e{sup +}e{sup -} storage ring. The {Lambda}{sub c}{sup +} mass is measured to be 2286.46 {+-} 0.14 MeV/c{sup 2}. The dominant systematic uncertainties arise from the amount of material in the tracking volume and from the magnetic field strength.
Date: July 6, 2005
Creator: Aubert, B.; Barate, R.; Boutigny, D.; Couderc, F.; Karyotakis, Y.; Lees, J. P. et al.
System: The UNT Digital Library
Search for B- -> Ds+(*)- Phi (open access)

Search for B- -> Ds+(*)- Phi

We report on searches for B{sup -} {yields} D{sub S}{sup -}{phi} and B{sup -} {yields} D*{sub S}{sup -}{phi}. In the context of the Standard Model the branching fractions for these decays are expected to be highly suppressed, since they proceed through annihilation of the b and {bar u} quarks in the B{sup -} meson. Our results are based on 234 million {Upsilon}(42) {yields} B{bar B} decays collected with the BABAR detector at SLAC. We find no evidence for these decays, and we set 90% confidence level upper limits on the branching fractions {Beta}(B{sup -} {yields} D{sub S}{sup -}{phi}) < 1.8 x 10{sup -6}; {Beta}(B{sup -} {yields} D*{sub S}{sup -}{phi}) < 1.1 x 10{sup -5}. These results are consistent with Standard Model expectations.
Date: July 6, 2005
Creator: Aubert, B.; Barate, R.; Boutigny, D.; Couderc, F.; Karyotakis, Y.; Lees, J. P. et al.
System: The UNT Digital Library
High-resolution ab-initio three-dimensional coherence X-ray diffraction microscopy (open access)

High-resolution ab-initio three-dimensional coherence X-ray diffraction microscopy

Three-dimensional diffraction microscopy offers the potential for high-resolution aberration-free diffraction-limited 3D images without the resolution and depth-of-field limitations of lens-based tomographic systems. Critical issues in obtaining a high-quality image include: (1) Data collection--signal to noise, system stability, dynamic range, automation; (2) Alignment of diffraction patterns with respect to one another; (3) Assembly of the diffraction data into a diffraction volume; and (4) Efficient algorithms for applying phase retrieval techniques to the diffraction volume; (5) Stability of the three-dimensional phase retrieval process; (6) Techniques for determining the object support; and (7) Treatment of missing data, both within the beamstop region and elsewhere. They have obtained high-quality 3D reconstructions from X-ray diffraction data alone. This is an important step, as it does not require a low-resolution image to fill in the beamstop region.
Date: June 6, 2005
Creator: Barty, A.
System: The UNT Digital Library
Measurement of Pressure Dependent Fluorescence Yield of Air: Calibration Factor for UHECR Detectors (open access)

Measurement of Pressure Dependent Fluorescence Yield of Air: Calibration Factor for UHECR Detectors

In a test experiment at the Final Focus Test Beam of the Stanford Linear Accelerator Center, the fluorescence yield of 28.5 GeV electrons in air and nitrogen was measured. The measured photon yields between 300 and 400 nm at 1 atm and 29 C are Y(760 Torr){sup air} = 4.42 {+-} 0.73 and Y(760 Torr){sup N{sub 2}} = 29.2 {+-} 4.8 photons per electron per meter. Assuming that the fluorescence yield is proportional to the energy deposition of a charged particle traveling through air, good agreement with measurements at lower particle energies is observed.
Date: July 6, 2005
Creator: Belz, J. W.; Burt, G. W.; Cao, Z.; Chang, F. Y.; Chen, C. C.; Chen, C. W. et al.
System: The UNT Digital Library
Dijet event shapes as diagnostic tools (open access)

Dijet event shapes as diagnostic tools

Event shapes have long been used to extract information about hadronic final states and the properties of QCD, such as particle spin and the running coupling. Recently, a family of event shapes, the angularities, has been introduced that depends on a continuous parameter. This additional parameter-dependence further extends the versatility of event shapes. It provides a handle on nonperturbative power corrections, on non-global logarithms, and on the flow of color in the final state.
Date: May 6, 2005
Creator: Berger, Carola F.
System: The UNT Digital Library
Bootstrapping Multi-Parton Loop Amplitudes in QCD (open access)

Bootstrapping Multi-Parton Loop Amplitudes in QCD

The authors present a new method for computing complete one-loop amplitudes, including their rational parts, in non-supersymmetric gauge theory. This method merges the unitarity method with on-shell recursion relations. It systematizes a unitarity-factorization bootstrap approach previously applied by the authors to the one-loop amplitudes required for next-to-leading order QCD corrections to the processes e{sup +}e{sup -} {yields} Z, {gamma}* {yields} 4 jets and pp {yields} W + 2 jets. We illustrate the method by reproducing the one-loop color-ordered five-gluon helicity amplitudes in QCD that interfere with the tree amplitude, namely A{sub 5;1}(1{sup -}, 2{sup -}, 3{sup +}, 4{sup +}, 5{sup +}) and A{sub 5;1}(1{sup -}, 2{sup +}, 3{sup -}, 4{sup +}, 5{sup +}). Then we describe the construction of the six- and seven-gluon amplitudes with two adjacent negative-helicity gluons, A{sub 6;1}(1{sup -}, 2{sup -}, 3{sup +}, 4{sup +}, 5{sup +}, 6{sup +}) and A{sub 7;1}(1{sup -}, 2{sup -}, 3{sup +}, 4{sup +}, 5{sup +}, 6{sup +}, 7{sup +}), which uses the previously-computed logarithmic parts of the amplitudes as input. They present a compact expression for the six-gluon amplitude. No loop integrals are required to obtain the rational parts.
Date: July 6, 2005
Creator: Bern, Zvi; Dixon, Lance J. & Kosower, David A.
System: The UNT Digital Library
Ignition Target Fabrication and Fielding for the National Ignition Facility (open access)

Ignition Target Fabrication and Fielding for the National Ignition Facility

Continued advances in the design of ignition targets have stimulating new development paths for target fabrication, with potentially important simplifications for fielding cryogenic ignition targets for the National Ignition Facility. Including graded dopants in ablators as well as optimizing capsule and fuel layer dimensions increase implosion stability. This has led to developments of micron-scale fill tubes to fill and field the targets. Rapid progress has been made in development of the graded dopant layers in capsules as well as their characterization, in fabrication methods for micro-fill-tubes, and in fuel fill control with these fill tubes. Phase-contrast x-ray radiography has allowed characterization of fuel layers in beryllium targets. This target development program includes participation from General Atomics, Lawrence Livermore National Laboratory, and Los Alamos National Laboratory.
Date: October 6, 2005
Creator: Bernat, T. P.; Huang, H.; Nikroo, A.; Stephens, R.; Wilkens, H.; Xu, H. et al.
System: The UNT Digital Library
Neutron Source Strength Estimates from (a, n) Reactions in Binary Mixtures of Actinide Particles and Light Element Particles (open access)

Neutron Source Strength Estimates from (a, n) Reactions in Binary Mixtures of Actinide Particles and Light Element Particles

The cumulative distribution of package dose rates, based on the 18 batches of historical PuO{sub 2} particle size distributions, is shown in Fig. 6 for ''Hanford 10-13% Pu-240'' plutonium. The calculated dose rates for all batches range from about 50 mrem/h to about 2,200 mrem/h, with over 50% of the batches being less than the 200 mrem/h limit for public transportation. A more refined analysis would show that almost all of the batches would be less than 200 mrem/h, but some could exceed this limit as seen by the distribution shape. Without detailed characterization of the BeO particle size distribution, additional analysis would not remove the uncertainty in these calculations. Because the actual amount of beryllium contamination is likely to be much less than 500 g, the dose rates would be expected to be much lower than those shown here. Based on the particle size distribution analysis of the 18 batches analyzed, it is also likely that most of the 3013 cans to be loaded in the 9975 Package will have dose rates that are less than the 200 mrem/h limit for the package surface. However, extra care will be required in performing, and verifying, the dose rate measurements at …
Date: May 6, 2005
Creator: Boles, J. L.; Hafner, R. S. & Fischer, L. E.
System: The UNT Digital Library
Recovery of Minerals and Metals from Geothermal Fluids (open access)

Recovery of Minerals and Metals from Geothermal Fluids

None
Date: September 6, 2005
Creator: Bourcier, W L; Lin, M & Nix, G
System: The UNT Digital Library
Stretched Wire Mechanics (open access)

Stretched Wire Mechanics

Stretched wires are beginning to play an important role in the alignment of accelerators and synchrotron light sources. Stretched wires are proposed for the alignment of the 130 meter long LCLS undulator. Wire position technology has reached sub-micron resolution yet analyses of perturbations to wire straightness are hard to find. This paper considers possible deviations of stretched wire from the simple 2-dimensional catenary form.
Date: September 6, 2005
Creator: Bowden, Gordon
System: The UNT Digital Library
Angularly Adaptive P1--Double P0 Diffusion Solutions of Non-Equilibrium Grey Radiative Transfer Problems in Planar Geometry (open access)

Angularly Adaptive P1--Double P0 Diffusion Solutions of Non-Equilibrium Grey Radiative Transfer Problems in Planar Geometry

The double spherical harmonics angular approximation in the lowest order, i.e. double P{sub 0} (DP{sub 0}), is developed for the solution of time-dependent non-equilibrium grey radiative transfer problems in planar geometry. The standard P{sub 1} angular approximation represents the angular dependence of the radiation specific intensity using a linear function in the angular domain -1 {le} {mu} {le} 1. In contrast, the DP{sub 0} angular approximation represents the angular dependence as isotropic in each half angular range -1 {le} {mu} < 0 and 0 < {mu} {le} 1. Neglecting the time derivative of the radiation flux, both the P{sub 1} and DP{sub 0} equations can be written as a single diffusion equation for the radiation energy density. Although the DP{sub 0} diffusion approximation is expected to be less accurate than the P{sub 1} diffusion approximation at and near thermodynamic equilibrium, the DP{sub 0} angular approximation can more accurately capture the complicated angular dependence near the non-equilibrium wave front. We develop an adaptive angular technique that locally uses either the DP{sub 0} or the P{sub 1} diffusion approximation depending on the degree to which the radiation and material fields are in thermodynamic equilibrium. Numerical results are presented for a test problem …
Date: June 6, 2005
Creator: Brantley, P S
System: The UNT Digital Library
Exploring Lifetime Effects in Femtoscopy (open access)

Exploring Lifetime Effects in Femtoscopy

We investigate the role of lifetime effects from resonances and emission duration tails in femtoscopy at RHIC in two Blast-Wave models. We find the non-Gaussian components compare well with published source imaged data, but the value of R{sub out} obtained from Gaussian fits is not insensitive to the non-Gaussian contributions when realistic acceptance cuts are applied to models.
Date: September 6, 2005
Creator: Brown, D.; Soltz, R.; Newby, J. & Kisiel, A.
System: The UNT Digital Library
Inductively Heated Shape Memory Polymer for the Magnetic Actuation of Medical Devices (open access)

Inductively Heated Shape Memory Polymer for the Magnetic Actuation of Medical Devices

Presently there is interest in making medical devices such as expandable stents and intravascular microactuators from shape memory polymer (SMP). One of the key challenges in realizing SMP medical devices is the implementation of a safe and effective method of thermally actuating various device geometries in vivo. A novel scheme of actuation by Curie-thermoregulated inductive heating is presented. Prototype medical devices made from SMP loaded with Nickel Zinc ferrite ferromagnetic particles were actuated in air by applying an alternating magnetic field to induce heating. Dynamic mechanical thermal analysis was performed on both the particle-loaded and neat SMP materials to assess the impact of the ferrite particles on the mechanical properties of the samples. Calorimetry was used to quantify the rate of heat generation as a function of particle size and volumetric loading of ferrite particles in the SMP. These tests demonstrated the feasibility of SMP actuation by inductive heating. Rapid and uniform heating was achieved in complex device geometries and particle loading up to 10% volume content did not interfere with the shape recovery of the SMP.
Date: September 6, 2005
Creator: Buckley, Patrick R.; McKinley, Gareth H.; Wilson, Thomas S.; Small, Ward, IV; Benett, William J.; Bearinger, Jane P. et al.
System: The UNT Digital Library
A First Look at Beam Diagnostics for the Rhic Electron Cooling Project. (open access)

A First Look at Beam Diagnostics for the Rhic Electron Cooling Project.

High energy electron cooling [1] is essential to meet the luminosity specification for RHIC II [2]. In preparation for electron cooling, an Energy Recovery Linac (ERL) test facility [3] is under construction at BNL. A preliminary description of Diagnostics for the ERL was presented at an earlier workshop [4]. A significant portion of the eCooling Diagnostics will be a simple extension of those developed for the ERL test facility. In this paper we present a preliminary report on eCooling Diagnostics. We summarize the planned conventional Diagnostics, and follow with more detailed descriptions of Diagnostics specialized to the requirements of high-energy magnetized cooling.
Date: June 6, 2005
Creator: Cameron, P.; Ben-Zvi, Ilan; Kewisch, J. & Litvinenko, V.
System: The UNT Digital Library
ADVANCES TOWARDS THE MEASUREMENT AND CONTROL LHC TUNE AND CHROMATICITY (open access)

ADVANCES TOWARDS THE MEASUREMENT AND CONTROL LHC TUNE AND CHROMATICITY

Requirements for tune and chromaticity control in most superconducting hadron machines, and in particular the LHC, are stringent. In order to reach nominal operation, the LHC will almost certainly require feedback on both tune and chromaticity. Experience at RHIC has also shown that coupling control is crucial to successful tune feedback. A prototype baseband phase-locked loop (PLL) tune measurement system has recently been brought into operation at RHIC as part of the US LHC Accelerator Research Program (LARP). We report on the performance of that system and compare it with the extensive accumulation of data from the RHIC 245MHz PLL.
Date: June 6, 2005
Creator: Cameron, P.; Cupolo, J.; Degen, C.; Dellapenna, A.; Hoff, L.; Mead, J. et al.
System: The UNT Digital Library
The Effects and Possible Origins of Mains Ripple in the Vicinity of the Betatron Spectrum. (open access)

The Effects and Possible Origins of Mains Ripple in the Vicinity of the Betatron Spectrum.

With the advent of significant improvement in the sensitivity of observation of the betatron spectrum, the appearance of spectral lines at harmonics of the mains power frequency has been observed in the PS and SPS at CERN, the Tevatron at FNAL, and RHIC at BNL. These lines are potentially problematic for accurate tune tracking and the implementation of tune feedback We discuss the possible origins of these lines, and present data to support our discussion.
Date: June 6, 2005
Creator: Cameron, P.; Gasior, M.; Jones, R. & Tan, C.
System: The UNT Digital Library
A Link between Meiotic Prophase Progression and CrossoverControl (open access)

A Link between Meiotic Prophase Progression and CrossoverControl

During meiosis, most organisms ensure that homologous chromosomes undergo at least one exchange of DNA, or crossover, to link chromosomes together and accomplish proper segregation. How each chromosome receives a minimum of one crossover is unknown. During early meiosis in Caenorhabditis elegans and many other species, chromosomes adopt a polarized organization within the nucleus, which normally disappears upon completion of homolog synapsis. Mutations that impair synapsis even between a single pair of chromosomes in C. elegans delay this nuclear reorganization. We quantified this delay by developing a classification scheme for discrete stages of meiosis. Immunofluorescence localization of RAD-51 protein revealed that delayed meiotic cells also contained persistent recombination intermediates. Through genetic analysis, we found that this cytological delay in meiotic progression requires double-strand breaks and the function of the crossover-promoting heteroduplex HIM-14 (Msh4) and MSH-5. Failure of X chromosome synapsis also resulted in impaired crossover control on autosomes, which may result from greater numbers and persistence of recombination intermediates in the delayed nuclei. We conclude that maturation of recombination events on chromosomes promotes meiotic progression, and is coupled to the regulation of crossover number and placement. Our results have broad implications for the interpretation of meiotic mutants, as we have …
Date: July 6, 2005
Creator: Carlton, Peter M.; Farruggio, Alfonso P. & Dernburg, Abby F.
System: The UNT Digital Library