951 research outputs found
Calculating the Charged Particle Stopping Power Exactly to Leading and Next-to-leading Order
I will discuss a new method for calculating transport quantities, such as the
charged particle stopping power, in a weakly to moderately coupled plasma. This
method, called dimensional continuation, lies within the framework of
convergent kinetic equations, and it is powerful enough to allow for systematic
perturbative expansions in the plasma coupling constant. In particular, it
provides an exact evaluation of the stopping power to leading and
next-to-leading order in the plasma coupling, with the systematic error being
of cubic order. Consequently, the calculation is near-exact for a weakly
coupled plasma, and quite accurate for a moderately coupled plasma. The leading
order term in this expansion has been known since the classic work of Spitzer.
In contrast, the next-to-leading order term has been calculated only recently
by Brown, Preston, and Singleton (BPS), using the aforementioned method, to
account for all short- and long-distance physics accurate to second order in
the plasma coupling, including an exact treatment of the quantum-to-classical
scattering transition. Preliminary numerical studies suggest that the BPS
stopping power increases the ignition threshold, thereby having potential
adverse implications for upcoming high energy density facilities. Since the key
ideas behind the BPS calculation are possibly unfamiliar to plasma physicists,
and the implications might be important, I will use this opportunity to explain
the method in a pedagogical fashion.Comment: 4 pages, proceedings for the 5th International Conference on Inertial
Fusion Science and Applications (IFSA-07), Kobe, Japan, 9-14 September 200
Optimal N-burn multiorbit injection
Procedure for computing gravity losses over n-burn multiorbit escape trajectories of specified final energy and prediction of optimal burn schedules for nuclear rocket escape maneuver
Wind-tunnel evaluation of an advanced main-rotor blade design for a utility-class helicopter
An investigation was conducted in the Langley Transonic Dynamics Tunnel to evaluate differences between an existing utility-class main-rotor blade and an advanced-design main-rotor blade. The two rotor blade designs were compared with regard to rotor performance oscillatory pitch-link loads, and 4-per-rev vertical fixed-system loads. Tests were conducted in hover and over a range of simulated full-scale gross weights and density altitude conditions at advance ratios from 0.15 to 0.40. Results indicate that the advanced blade design offers performance improvements over the baseline blade in both hover and forward flight. Pitch-link oscillatory loads for the baseline rotor were more sensitive to the test conditions than those of the advanced rotor. The 4-per-rev vertical fixed-system load produced by the advanced blade was larger than that produced by the baseline blade at all test conditions
Isgur-Wise Functions from the Mit Bag Model
The Isgur-Wise functions for the ground state to ground state semileptonic
decays involving transitions are calculated from the
(modified) MIT bag model. It is checked that the results for the decays
and agree well with experiment. Predictions for the decays , and are given
and discussed.Comment: 12 pages (3 figures available upon request), LaTeX, TPJU - 9/9
Evidence of Andreev bound states as a hallmark of the FFLO phase in -(BEDT-TTF)Cu(NCS)
Superconductivity is a quantum phenomena arising, in its simplest form, from
pairing of fermions with opposite spin into a state with zero net momentum.
Whether superconductivity can occur in fermionic systems with unequal number of
two species distinguished by spin, atomic hyperfine states, flavor, presents an
important open question in condensed matter, cold atoms, and quantum
chromodynamics, physics. In the former case the imbalance between spin-up and
spin-down electrons forming the Cooper pairs is indyced by the magnetic field.
Nearly fifty years ago Fulde, Ferrell, Larkin and Ovchinnikov (FFLO) proposed
that such imbalanced system can lead to exotic superconductivity in which pairs
acquire finite momentum. The finite pair momentum leads to spatially
inhomogeneous state consisting of of a periodic alternation of "normal" and
"superconducting" regions. Here, we report nuclear magnetic resonance (NMR)
measurements providing microscopic evidence for the existence of this new
superconducting state through the observation of spin-polarized quasiparticles
forming so-called Andreev bound states.Comment: 6 pages, 5 fig
Mutation Frequency of the Major Frontotemporal Dementia Genes, MAPT, GRN and C9ORF72 in a Turkish Cohort of Dementia Patients
‘Microtubule-associated protein tau’ (MAPT), ‘granulin’ (GRN) and ‘chromosome 9 open reading frame72’ (C9ORF72) gene mutations are the major known genetic causes of frontotemporal dementia (FTD). Recent studies suggest that mutations in these genes may also be associated with other forms of dementia. Therefore we investigated whether MAPT, GRN and C9ORF72 gene mutations are major contributors to dementia in a random, unselected Turkish cohort of dementia patients. A combination of whole-exome sequencing, Sanger sequencing and fragment analysis/Southern blot was performed in order to identify pathogenic mutations and novel variants in these genes as well as other FTD-related genes such as the ‘charged multivesicular body protein 2B’ (CHMP2B), the ‘FUS RNA binding protein’ (FUS), the ‘TAR DNA binding protein’ (TARDBP), the ‘sequestosome1’ (SQSTM1), and the ‘valosin containing protein’ (VCP). We determined one pathogenic MAPT mutation (c.1906C>T, p.P636L) and one novel missense variant (c.38A>G, p.D13G). In GRN we identified a probably pathogenic TGAG deletion in the splice donor site of exon 6. Three patients were found to carry the GGGGCC expansions in the non-coding region of the C9ORF72 gene. In summary, a complete screening for mutations in MAPT, GRN and C9ORF72 genes revealed a frequency of 5.4% of pathogenic mutations in a random cohort of 93 Turkish index patients with dementia
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