Telomere structure, replication and length maintenance

Telomeres are the termini of linear eukaryotic chromosomes consisting of tandem repeats of DNA and proteins that bind to these repeat sequences. Telomeres ensure the complete replication of chromosome ends, impart protection to ends from nucleolytic degradation, end-to-end fusion, and guide the localization of chromosomes within the nucleus. In addition, a combination of genetic, biochemical, and molecular biological approaches have implicated key roles for telomeres in diverse cellular processes such as regulation of gene expression, cell division, cell senescence, and cancer. This review focuses on recent advances in our understanding of the organization of telomeres, telomere replication, proteins that bind telomeric DNA, and the establishment of telomere length equilibrium.

Vortex dynamics at rf frequencies in Bi2Sr2CaCu2O8 single crystals

We have studied the low magnetic field high temperature region of the H-T phase diagram of Bi2Sr2CaCu2O8 single crystals using the technique of non-resonant rf response at a frequency of 20 MHz. With H(rf)parallel to a, H parallel to c, the isothermal magnetic field scans below T-c show that the frequency f(H) of the tank circuit decreases continuously with increase in H before saturating at H similar to H-D(T). Such a decrease in f(H) reflects increasing rf penetration into the weakly screened region between CuO bilayers. The saturation of f(H) at its lowest value for H similar to H-D(T) indicates complete rf penetration land hence the disappearance of field dependence) due to the vanishing of the screening rf currents I-rf(c) in those regions or equivalently when the phase coherence between adjacent superconducting layers vanishes. Therefore H,(T) represents the decoupling of the adjacent superconducting bilayers, and hence also a 3D to 2D decoupling transition of the vortex structure. Simultaneous monitoring of the field dependent rf power dissipation P(H) shows a maximum in dP/dH at H-D(T). The observed H-D(T) line in many crystals is in excellent agreement with the (l/t-1) behavior proposed for decoupling.

Finite Element Solution Of Surface-Tension Driven Flows In Laser Surface-Melting

Lasers are very efficient in heating localized regions and hence they find a wide application in surface treatment processes. The surface of a material can be selectively modified to give superior wear and corrosion resistance. In laser surface-melting and welding problems, the high temperature gradient prevailing in the free surface induces a surface-tension gradient which is the dominant driving force for convection (known as thermo-capillary or Marangoni convection). It has been reported that the surface-tension driven convection plays a dominant role in determining the melt pool shape. In most of the earlier works on laser-melting and related problems, the finite difference method (FDM) has been used to solve the Navier Stokes equations [1]. Since the Reynolds number is quite high in these cases, upwinding has been used. Though upwinding gives physically realistic solutions even on a coarse grid, the results are inaccurate. McLay and Carey have solved the thermo-capillary flow in welding problems by an implicit finite element method [2]. They used the conventional Galerkin finite element method (FEM) which requires that the pressure be interpolated by one order lower than velocity (mixed interpolation). This restricts the choice of elements to certain higher order elements which need numerical integration for evaluation of element matrices. The implicit algorithm yields a system of nonlinear, unsymmetric equations which are not positive definite. Computations would be possible only with large mainframe computers.Sluzalec [3] has modeled the pulsed laser-melting problem by an explicit method (FEM). He has used the six-node triangular element with mixed interpolation. Since he has considered the buoyancy induced flow only, the velocity values are small. In the present work, an equal order explicit FEM is used to compute the thermo-capillary flow in the laser surface-melting problem. As this method permits equal order interpolation, there is no restriction in the choice of elements. Even linear elements such as the three-node triangular elements can be used. As the governing equations are solved in a sequential manner, the computer memory requirement is less. The finite element formulation is discussed in this paper along with typical numerical results.

Oded Schramm and the Schramm-Loewner evolution: In memoriam

Oded Schramm, the inventor of the stochastic Loewner evolution (SLE), died on 1 September 2008 in a tragic hiking accident in the Cascades Mountains. He was forty-six. He is survived by his wife and two children.

On the nature of power flow equations in security analysis

The power system network is assumed to be in steady-state even during low frequency transients. However, depending on generator dynamics, and toad and control characteristics, the system model and the nature of power flow equations can vary The nature of power flow equations describing the system during a contingency is investigated in detail. It is shown that under some mild assumptions on load-voltage characteristics, the power flow equations can be decoupled in an exact manner. When the generator dynamics are considered, the solutions for the load voltages are exact if load nodes are not directly connected to each other

The connection between Mueller and Jones matrices of polarization optics

A necessary and sufficient condition for the 4 × 4 Mueller matrix to be derivable from the 2 × 2 Jones matrix is obtained. This condition allows one to determine if a given Mueller matrix describes a totally polarized system or a partially polarized (depolarizing) system. The result of Barakat is analysed in the light of this condition. A recently reported experimentally measured Mueller matrix is examined using this condition and is shown to represent a partially polarized system.

Structure of 4-Hydroxymonophenylbutazone

4-Butyl-4-hydroxy-l-phenyl-3,5-pyrazolidinedione, ClaH16N20 a, Mr=248.3, monoclinic, P21/n, a = 22.357 (5), b = 5.014 (2), c = 11.350 (4)/~,, //=91.88(3) °, V=1272(1)A 3, Z=4, D,,=1.296(3), D x = 1.297 Mg m -3, 2(Cu Ka) = 1.5418/~, a = 0.777 mm -~, F(000) = 528, T= 293 K. Final R - 0.059 for 1668 observed reflections. The hetero nitrogen which carries the six-membered ring is planar in the structure while the other unsubstituted one is pyramidal. The five- and six-membered rings are almost coplanar. The crystal is made up of infinite columns of hydrogen-bonded molecules.

A linear root water uptake model

A model of root water extraction is proposed, in which a linear variation of extraction rate with depth is assumed. Five crops are chosen for simulation studies of the model, and soil moisture depletion under optimal conditions from different layers for each crop is calculated. Similar calculations are also made using the constant extraction rate model. Rooting depth is assumed to vary linearly with potential evapotranspiration for each crop during the vegetative phase. The calculated depletion patterns are compared with measured mean depletion patterns for each crop. It is shown that the constant extraction rate model results in large errors in the prediction of soil moisture depletion, while the proposed linear extraction rate model gives satisfactory results. Hypothetical depletion patterns predicted by the model in combination with a moisture tension-dependent sink term developed elsewhere are indicated.

Crystal and molecular structures of alkali- and alkaline-earth-metal complexes of N,N-dimethylformamide

Structures of lithium, sodium, magnesium, and calcium complexes of NJ-dimethylformamide (DMF) have been investigated by X-ray crystallography. Complexes with the formulas LiCl.DMF.1/2H20, NaC104.2DMF, CaC12.2DMF.2H20, and Mg(C104)2.6DMF crystallized in space groups P2]/c, P2/c, Pi, and Ella, respectively, with the following cell dimensions: Li complex, a = 13.022 (7) A, b = 5.978 (4) A, c = 17.028 (10) A, = 105.48 (4)O, Z = 8; Na complex, a = 9.297 (4)A, b = 10.203 (3) A, c = 13.510 (6) A, /3 = 110.08 (4)O, Z = 4; Ca complex, a = 6.293 (4) A, b = 6.944 (2) A, c = 8.853(5) A, a = 110.15 (3)O, /3 = 105.60 (6)", y = 95.34 (5)", Z = 1; Mg complex, a = 20.686 (11) A, b = 10.962 (18) A,c = 14.885 (9) A, /3 = 91.45 (5)O, Z = 4. Lithium is tetrahedrally coordinated while the other three cations are octahedrally coordinated; the observed metal-oxygen distances are within the ranges generally found in oxygen donor complexes of these metals. The lithium and sodium complexes are polymeric, with the amide and the anion forming bridging groups between neighboring cations. The carbonyl distances become longer in the complexes accompanied by a proportionate decrease in the length of the central C-N bond of the amide; the N-C bond of the dimethylamino group also shows some changes in the complexes. The cations do not deviate significantly from the lone-pair direction of the amide carbonyl and remain in the amide plane. Infrared spectra of the complexes reflect the observed changes in the amide bond distances.

Assessment of accuracies of some approximate solutions

The classic work of Richardson and Gaunt [1 ], has provided an effective means of extrapolating the limiting result in an approximate analysis. From the authors' work on "Bounds for eigenvalues" [2-4] an interesting alternate method has emerged for assessing monotonically convergent approximate solutions by generating close bounds. Whereas further investigation is needed to put this work on sound theoretical foundation, we intend this letter to announce a possibility, which was confirmed by an exhaustive set of examples.

4-Biphenylyl phenyl thioketone (I), C19H14S, and 1-naphthyl phenyl thioketone (II), C17H12S

(I): Mr=274"39, orthorhombic, Pbca, a = 7.443 (1), b= 32.691 (3), c= 11.828 (2)A, V= 2877.98A 3, Z=8, Din= 1.216 (flotation in KI), D x = 1.266 g cm -3, /~(Cu Ka, 2 = 1.5418 A) = 17.55 cm -1, F(000) = li52.0, T= 293 K, R = 6.8%, 1378 significant reflections. (II): M r = 248.35, orthorhombic, P212~21, a = 5.873 (3), b = 13.677 (3), c = 15-668 (5) A, V = 1260.14 A 3, Z = 4, D,n = 1.297 (flotation in KI), Dx= 1.308 g cm -a, /t(CuKa, 2=1.5418 A) = 19.55 cm -~, F(000) = 520.0, T= 293 K, R = 6.9%, 751 significant reflections. Crystals of (I) and (II) undergo photo-oxidation in the crystallinestate. In (I) the dihedral angle between the phenyl rings of the biphenyl moiety is 46 (1) °. The C=S bond length is 1.611(5) A in (I) and 1.630 (9)/~ in (II). The correlation between molecular packing and reactivity is discussed.

Measurement of sensitivities for the thermal recording of laser beams

A simple technique for determining the energy sensitivities for the thermographic recording of laser beams is described. The principle behind this technique is that, if a laser beam with a known spatial distribution such as a Gaussian profile is used for imaging, the radius of the thermal image formed depends uniquely on the intensity of the impinging beam. Thus by measuring the radii of the images produced for different incident beam intensities the minimum intensity necessary (that is, the threshold) for thermographic imaging is found. The diameter of the laser beam can also be found from this measurement. A simple analysis based on the temperature distribution in the laser heated material shows that there is an inverse square root dependence on pulse duration or period of exposure for the energy fluence of the laser beam required, both for the threshold and the subsequent increase in the size of the recording. It has also been shown that except for low intensity, long duration exposure on very low conductivity materials, heat losses are not very significant.

Polyvanadate-stimulated NADH oxidation by plasma membranes-The need for a mixture of deca and meta forms of vanadate

Polyvanadate solutions obtained by extracting vanadium pentoxide with dilute alkali over a period of several hours contained increasing amounts of decavanadate as characterized by NMR and ir spectra. Those solutions having a metavanadate:decavanadate ratio in the range of 1-5 showed maximum stimulation of NADH oxidation by rat liver plasma membranes. Reduction of decavanadate, but not metavanadate, was obtained only in the presence of the plasma membrane enzyme system. High simulation of activity of NADH oxidation was obtained with a mixture of the two forms of vanadate and this further increased on lowering the pH. Addition of increasing concentrations of decavanadate to metavanadate and vice versa increased the stimulatory activity, reaching a maximum when the metavanadate:decavanadate ratio was in the range of 1-5. Increased stimulatory activity can also be obtained by reaching these ratios by conversion of decavanadate to metavanadate by alkaline phosphate degradation, and of metavanadate to decavanadate by acidification. These studies show for the first time that both deca and meta forms of vanadate present in polyvanadate solutions are needed for maximum activity of NADH oxidation.

Reactivity of µ-Peroxo-Bridged Dimeric Vanadate in Bromoperoxidation

Diglycyl triperoxodivanadate [V2O2(O2)3(Gly H)2(H2O)2], a synthetic compound with μ-peroxo-bridge derived from H2O2and vanadate, oxidized bromide to a bromination-competent intermediate in phosphate buffer and physiological pH. This is in contrast to the requirement of acid medium with H2O2as the oxidant. Addition of its solid to bromide solution instantly produced a 262-nm-absorbing compound that converted phenol red (a trap) to its 592-nm-absorbing bromo-derivative. The high bromination activity was lost on dissolving this compound in water and the solution showed the presence of peroxovanadates (mono and di) and vanadates (V1and oligomeric V10) in51V-NMR spectrum. Of these, diperoxovanadate and vanadate together supported slow bromination activity by a second set of reactions including bromide-assisted reductive formation of vanadyl. Bromination activity dependent on vanadyl was sensitive to oxidation by excess H2O2and to complexation by EDTA, whereas that of triperoxodivanadate was relatively insensitive. Vanadyl and diperoxovanadate are capable of forming a μ-peroxo-bridged complex that is essentially similar to the synthetic vanadate dimer used in the present experiments. It appears that a μ-peroxo-intermediate is the proximal oxidant of bromide in vanadium-catalyzed bromoperoxidation.