Remnants of dark matter clumps

What happened to the central cores of tidally destructed dark matter clumps in the Galactic halo? We calculate the probability of surviving of the remnants of dark matter clumps in the Galaxy by modelling the tidal destruction of the small-scale clumps. It is demonstrated that a substantial fraction of clump remnants may survive through the tidal destruction during the lifetime of the Galaxy if the radius of a core is rather small. The resulting mass spectrum of survived clumps is extended down to the mass of the core of the cosmologically produced clumps with a minimal mass. Since the annihilation signal is dominated by the dense part of the core, destruction of the outer part of the clump affects the annihilation rate relatively weakly and the survived dense remnants of tidally destructed clumps provide a large contribution to the annihilation signal in the Galaxy. The uncertainties in minimal clump mass resulting from the uncertainties in neutralino models are discussed.Comment: 13 pages, 6 figures, added reference

Nonuniform Self-Organized Dynamical States in Superconductors with Periodic Pinning

We consider magnetic flux moving in superconductors with periodic pinning arrays. We show that sample heating by moving vortices produces negative differential resistivity (NDR) of both N and S type (i.e., N- and S-shaped) in the voltage-current characteristic (VI curve). The uniform flux flow state is unstable in the NDR region of the VI curve. Domain structures appear during the NDR part of the VI curve of an N type, while a filamentary instability is observed for the NDR of an S type. The simultaneous existence of the NDR of both types gives rise to the appearance of striking self-organized (both stationary and non-stationary) two-dimensional dynamical structures.Comment: 4 pages, 2 figure

Negative differential resistivity in superconductors with periodic arrays of pinning sites

We study theoretically the effects of heating on the magnetic flux moving in superconductors with a periodic array of pinning sites (PAPS). The voltage-current characteristic (VI-curve) of superconductors with a PAPS includes a region with negative differential resistivity (NDR) of S-type (i.e., S-shaped VI-curve), while the heating of the superconductor by moving flux lines produces NDR of N-type (i.e., with an N-shaped VI-curve). We analyze the instability of the uniform flux flow corresponding to different parts of the VI-curve with NDR. Especially, we focus on the appearance of the filamentary instability that corresponds to an S-type NDR, which is extremely unusual for superconductors. We argue that the simultaneous existence of NDR of both N- and S-type gives rise to the appearance of self-organized two-dimensional dynamical structures in the flux flow mode. We study the effect of the pinning site positional disorder on the NDR and show that moderate disorder does not change the predicted results, while strong disorder completely suppresses the S-type NDR.Comment: 10 pages, 1 table, 7 figure

Small-scale clumps in the galactic halo and dark matter annihilation

Production of small-scale DM clumps is studied in the standard cosmological scenario with an inflation-produced primeval fluctuation spectrum. Special attention is given to three following problems: (i) The mass spectrum of small-scale clumps with $M \lesssim 10^3 M_{\odot}$ is calculated with tidal destruction of the clumps taken into account within the hierarchical model of clump structure. Only 0.1 - 0.5% of small clumps survive the stage of tidal destruction in each logarithmic mass interval $\Delta\ln M\sim1$. (ii) The mass distribution of clumps has a cutoff at $M_{\rm min}$ due to diffusion of DM particles out of a fluctuation and free streaming at later stage. $M_{\rm min}$ is a model dependent quantity. In the case the neutralino, considered as a pure bino, is a DM particle, $M_{\rm min} \sim 10^{-8} M_{\odot}$. (iii) The evolution of density profile in a DM clump does not result in the singularity because of formation of the core under influence of tidal interaction. The radius of the core is $R_c \sim 0.1 R$, where $R$ is radius of the clump. The applications for annihilation of DM particles in the Galactic halo are studied. The number density of clumps as a function of their mass, radius and distance to the Galactic center is presented. The enhancement of annihilation signal due to clumpiness, valid for arbitrary DM particles, is calculated. In spite of small survival probability, the annihilation signal in most cases is dominated by clumps. For observationally preferable value of index or primeval fluctuation spectrum $n_p \approx 1$, the enhancement of annihilation signal is described by factor 2 - 5 for different density profiles in a clump.Comment: inor changes in text and 2 references adde

A Switch from a Gradient to a Threshold Mode in the Regulation of a Transcriptional Cascade Promotes Robust Execution of Meiosis in Budding Yeast

Tight regulation of developmental pathways is of critical importance to all organisms, and is achieved by a transcriptional cascade ensuring the coordinated expression of sets of genes. We aimed to explore whether a strong signal is required to enter and complete a developmental pathway, by using meiosis in budding yeast as a model. We demonstrate that meiosis in budding yeast is insensitive to drastic changes in the levels of its consecutive positive regulators (Ime1, Ime2, and Ndt80). Entry into DNA replication is not correlated with the time of transcription of the early genes that regulate this event. Entry into nuclear division is directly regulated by the time of transcription of the middle genes, as premature transcription of their activator NDT80, leads to a premature entry into the first meiotic division, and loss of coordination between DNA replication and nuclear division. We demonstrate that Cdk1/Cln3 functions as a negative regulator of Ime2, and that ectopic expression of Cln3 delays entry into nuclear division as well as NDT80 transcription. Because Ime2 functions as a positive regulator for premeiotic DNA replication and NDT80 transcription, as well as a negative regulator of Cdk/Cln, we suggest that a double negative feedback loop between Ime2 and Cdk1/Cln3 promotes a bistable switch from the cell cycle to meiosis. Moreover, our results suggest a regulatory mode switch that ensures robust meiosis as the transcription of the early meiosis-specific genes responds in a graded mode to Ime1 levels, whereas that of the middle and late genes as well as initiation of DNA replication, are regulated in a threshold mode

Ectopic overexpresion of Cln3 increases the transcription of <i>IME1</i>, but delays initiation of premeiotic DNA replication and <i>NDT80</i> transcription.

<p>A wt strain (Y1631) carrying <i>pIME2-CLN3</i> on a 2μ plasmid (YEp3212, triangles) or the vector plasmid (squares) were shifted to meiotic conditions. At the indicated hours samples were taken to process for FACS analysis and calculate the percentage of cells with 4C DNA content (A), and to isolate RNA and determine the relative transcripts levels of <i>IME1</i> and <i>NDT80</i> by qPCR (B).</p

The level of <i>IME1</i> affects the time cells initiate premeiotic DNA replication, recombination and nuclear division.

<p>Isogenic diploids carrying different copy numbers of <i>IME1</i> were shifted to meiotic conditions. Samples were taken at the indicated times for FACS analysis and to calculate the percentage of cells with 4C DNA content (A), to plate on minus adenine medium and YEPD to measure the level of intragenic recombination at the <i>ADE2</i> locus (B), and to stain with DAPI to count the percentage of cells with more than 2 nuclei (C).</p

Meiosis is insensitive to the level of <i>IME1</i> mRNA.

<p>Isogenic diploids carrying different copy numbers of <i>IME1</i> were shifted to meiotic inducing conditions. <b>A.</b> The correlation between <i>IME1</i> copy number and its maximal level of expression. The maximal level of <i>IME1</i> RNA (from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0011005#pone-0011005-g003" target="_blank">Fig. 3A</a>) in comparison to the copy number of the <i>IME1</i> gene was drawn. The fitted trend line (dotted) and its formula are given. <b>B.</b> Efficiency of meiosis. The percentage of asci (line) and the number of cells that can form colonies (viability, column) at 48 hours in SPM. The results are the averages of three independent transformants and a count of ≥200 cells. Error bars represent standard deviations.</p

A schematic model illustrating the transcriptional cascade that governs meiosis in <i>S. cerevisiae</i>.

<p>A schematic model illustrating the transcriptional cascade that governs meiosis in <i>S. cerevisiae</i>.</p