Large-Area, Low-Noise, High Speed, Photodiode-Based Fluorescence Detectors with Fast Overdrive Recovery

Two large-area, low noise, high speed fluorescence detectors have been built. One detector consists of a photodiode with an area of 28 mm x 28 mm and a low noise transimpedance amplifier. This detector has a input light-equivalent spectral noise density of less than 3 pW/Hz^1/2, can recover from a large scattered light pulse within 10 us, and has a bandwidth of at least 900 kHz. The second detector consists of a 16 mm diameter avalanche photodiode and a low-noise transimpedance amplifier. This detector has an input light-equivalent spectral noise density of 0.08 pW/Hz^1/2, also can recover from a large scattered light pulse within 10 us, and has a bandwidth of 1 MHz.Comment: Submitted to Review of Scientific Instrument

Greybody factor for the BTZ black hole and a 5D black hole

We study the 5D black holes in the type IIB superstring theory compactified on $S^1 \times T^4$. Far from horizon, we have flat space-time. Near horizon, we have $AdS_3(BTZ black hole) \times S^3 \times T^4$. We calculate the greybody factor of a minimally coupled scalar by replacing the original geometry($M_5 \times S^1 \times T^4$) by $AdS_3 \times S^3 \times T^4$. In the low-energy scattering, it turns out that the result agrees with the greybody factor of the 5D black hole (or D1 + D5 branes)in the dilute gas approximation. This confirms that the $AdS$-theory($AdS_3 \times S^3 \times T^4$) contains the essential information about the bulk 5D black holes.Comment: some discussions are added, 15 Pages, No figure, RevTe

Diffusion of Neon in White Dwarf Stars

Sedimentation of the neutron rich isotope $^{22}$Ne may be an important source of gravitational energy during the cooling of white dwarf stars. This depends on the diffusion constant for $^{22}$Ne in strongly coupled plasma mixtures. We calculate self-diffusion constants $D_i$ from molecular dynamics simulations of carbon, oxygen, and neon mixtures. We find that $D_i$ in a mixture does not differ greatly from earlier one component plasma results. For strong coupling (coulomb parameter $\Gamma>$ few), $D_i$ has a modest dependence on the charge $Z_i$ of the ion species, $D_i \propto Z_i^{-2/3}$. However $D_i$ depends more strongly on $Z_i$ for weak coupling (smaller $\Gamma$). We conclude that the self-diffusion constant $D_{\rm Ne}$ for $^{22}$Ne in carbon, oxygen, and neon plasma mixtures is accurately known so that uncertainties in $D_{\rm Ne}$ should be unimportant for simulations of white dwarf cooling.Comment: 6 pages, 5 figures, minor changes, Phys. Rev. E in pres

Where is the Information Stored in Black Holes?

It is shown that many modes of the gravitational field exist only inside the horizon of an extreme black hole in string theory. At least in certain cases, the number of such modes is sufficient to account for the Bekenstein-Hawking entropy. These modes are associated with sources which carry Ramond-Ramond charge, and so may be viewed as the strong coupling limit of D-branes. Although these sources naturally live at the singularity, they are well defined and generate modes which extend out to the horizon. This suggests that the information in an extreme black hole is not localized near the singularity or the horizon, but extends between them.Comment: 21 pages, reference corrected and comment adde

Crystallization of Carbon Oxygen Mixtures in White Dwarf Stars

We determine the phase diagram for dense carbon/ oxygen mixtures in White Dwarf (WD) star interiors using molecular dynamics simulations involving liquid and solid phases. Our phase diagram agrees well with predictions from Ogata et al. and Medin and Cumming and gives lower melting temperatures than Segretain et al. Observations of WD crystallization in the globular cluster NGC 6397 by Winget et al. suggest that the melting temperature of WD cores is close to that for pure carbon. If this is true, our phase diagram implies that the central oxygen abundance in these stars is less than about 60%. This constraint, along with assumptions about convection in stellar evolution models, limits the effective S factor for the $^{12}$C($\alpha,\gamma$)$^{16}$O reaction to S_{300} <= 170 keV barns.Comment: 4 pages, 2 figures, Phys. Rev. Lett. in pres

A human protein required for the second step of pre-mRNA splicing is functionally related to a yeast splicing factor

We have identified a human splicing factor required for the second step of pre-mRNA splicing. This new protein, hPrp18, is 30% identical to the yeast splicing factor Prp18. In HeLa cell extracts immunodepleted of hPrp18, the second step of pre-mRNA splicing is abolished. Splicing activity is restored by the addition of recombinant hPrp18, demonstrating that hPrp18 is required for the second step. The hPrp18 protein is bound tightly to the spliceosome only during the second step of splicing. hPrp18 is required for the splicing of several pre-mRNAs, making it the first general second-step splicing factor found in humans. Splicing activity can be restored to hPrp18-depleted HeLa cell extracts by yeast Prp18, showing that important functional regions of the proteins have been conserved. A 90-amino-acid region near the carboxyl terminus of hPrp18 is strongly homologous to yeast Prp18 and is also conserved in rice and nematodes. The homology identifies one region important for the function of both proteins and may define a new protein motif. In contrast to yeast Prp18, hPrp18 is not stably associated with any of the snRNPs. A 55-kD protein that cross-reacts with antibodies against hPrp18 is a constituent of the U4/U6 and U4/U6 . U5 snRNP particles

Strong Correlations in Actinide Redox Reactions

Reduction-oxidation (redox) reactions of the redox couples An(VI)/An(V), An(V)/An(IV), and An(IV)/An(III), where An is an element in the family of early actinides (U, Np, and Pu), as well as Am(VI)/Am(V) and Am(V)/Am(III), are modeled by combining density functional theory with a generalized Anderson impurity model that accounts for the strong correlations between the 5f electrons. Diagonalization of the Anderson impurity model yields improved estimates for the redox potentials and the propensity of the actinide complexes to disproportionate.Comment: 17 pages, 10 figure, 3 tables. Corrections and clarifications; this version has been accepted for publication in The Journal of Chemical Physic