7,223 research outputs found
Remarks on the instability of black Dp-branes
We show that for black D-branes having charge and Hawking temperature
, the product is bounded from above for and is
unbounded for . While the maximum occurs at some finite value of a
parameter for , it occurs at infinity of the parameter for . As
a consequence, for fixed charge, there are two black D-branes (for ) at any given temperature less than its maximum value, and when the
temperature is maximum there is one black D-brane. For , there is only
one black D5-brane at a given temperature less than its maximum value, whereas,
for , since there is no bound for the temperature, there is always a black
D6-brane solution at a given temperature. Of the two black D-branes (for
), one is large which is shown to be thermodynamically unstable and
the other is small which is stable. But for , the black D-branes are
always thermodynamically unstable. The stable, small black D-brane, however,
under certain conditions, can become unstable quantum mechanically and decay
either to a BPS D-brane or to a Kaluza-Klein "bubble of nothing" through
closed string tachyon condensation. The small D5, D6 branes, although
classically unstable, have the same fate under similar conditions.Comment: 12 pages, LaTeX, 1 figure, v2: minor clarifications added, v3: added
free energy calculation, version to appear in Phys. Lett.
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Linking Aboveground Traits to Root Traits and Local Environment: Implications of the Plant Economics Spectrum.
The plant economics spectrum proposes that ecological traits are functionally coordinated and adapt along environmental gradients. However, empirical evidence is mixed about whether aboveground and root traits are consistently linked and which environmental factors drive functional responses. Here we measure the strength of relationships between aboveground and root traits, and examine whether community-weighted mean trait values are adapted along gradients of light and soil fertility, based on the seedling censuses of 57 species in a subtropical forest. We found that aboveground traits were good predictors of root traits; specific leaf area, dry matter, nitrogen and phosphorus content were strongly correlated with root tissue density and specific root length. Traits showed patterns of adaptation along the gradients of soil fertility and light; species with fast resource-acquisitive strategies were more strongly associated with high soil phosphorus, potassium, openness, and with low nitrogen, organic matter conditions. This demonstrates the potential to estimate belowground traits from known aboveground traits in seedling communities, and suggests that soil fertility is one of the main factors driving functional responses. Our results extend our understanding of how ecological strategies shape potential responses of plant communities to environmental change
Alkyl-Alkyl Suzuki Cross-Coupling of Unactivated Secondary Alkyl Chlorides
No such thing as a problem substrate! In a reaction designed specifically for the title substrates C-C coupling with alkyl boranes occurred in good yield at room temperature with commercially available catalyst components (see scheme). This versatile method is also suitable for Suzuki reactions of secondary and primary alkyl bromides and iodides, as well as primary alkyl chlorides.National Institute of General Medical Sciences (U.S.) (Grant R01-GM62871)Eli Lilly and Company (Fellowship)Martin Family Society of Fellows for Sustainability (Fellowship)Merck Research LaboratoriesNovartis (Firm
Alkyl-Alkyl Suzuki Cross-Coupling of Unactivated Secondary Alkyl Chlorides
No such thing as a problem substrate! In a reaction designed specifically for the title substrates C-C coupling with alkyl boranes occurred in good yield at room temperature with commercially available catalyst components (see scheme). This versatile method is also suitable for Suzuki reactions of secondary and primary alkyl bromides and iodides, as well as primary alkyl chlorides
New total transmission modes of the Kerr geometry with Schwarzschild limit frequencies at complex infinity
In addition to the well-known quasinormal modes, the gravitational modes of
the Kerr geometry also include sets of total-transmission modes. Each mode can
be considered as an element of a sequence of modes parameterized by the angular
momentum of the black hole. One family of gravitational total-transmission
modes of Kerr have been known for some time. Modes in this family connect to a
Schwarzschild limit where the mode frequency is finite and purely imaginary.
Recently, what was thought to be an additional branch of this original family
of modes was discovered. However, this new branch is actually a part of one of
two entirely new families of total-transmission modes. Modes in these new
families, surprisingly, connect to a Schwarzschild limit where the mode
frequencies exist at complex infinity. We have numerically constructed full
sets of sequences of gravitational total-transmission modes for harmonic
indices . Using these numerical sequences, we have been able to
construct analytic asymptotic expansions for the mode frequencies and their
associated separation constants. The asymptotic expansion for the separation
constant used in constructing the total-transmission modes seems to be valid
for general complex values of the oblateness parameter.Comment: 19 pages, 13 figures, 5 table
Applying Derivative-Free Optimization to Fit Kinetic Parameters of Viral Capsid Self-Assembly Models from Multi-Source Bulk in vitro Data
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