5,897 research outputs found
Setting the quantum integrand of M-theory
In anomaly-free quantum field theories the integrand in the bosonic
functional integral--the exponential of the effective action after integrating
out fermions--is often defined only up to a phase without an additional choice.
We term this choice ``setting the quantum integrand''. In the low-energy
approximation to M-theory the E(8)-model for the C-field allows us to set the
quantum integrand using geometric index theory. We derive mathematical results
of independent interest about pfaffians of Dirac operators in 8k+3 dimensions,
both on closed manifolds and manifolds with boundary. These theorems are used
to set the quantum integrand of M-theory for closed manifolds and for compact
manifolds with either temporal (global) or spatial (local) boundary conditions.
In particular, we show that M-theory makes sense on arbitrary 11-manifolds with
spatial boundary, generalizing the construction of heterotic M-theory on
cylinders.Comment: 52 pages; revised version for publication in Commun. Math. Phys.
corrects a few typo
Lead salt diode lasers and development of tunable solid state lasers for remote sensing
Extensive studies of the output characteristics of single quantum well lead-telluride lasers developed at the General Motors Research Laboratories were carried out. Threshold currents, output powers and line structures were measured as a function of temperature. Very low-current lasing thresholds, record high operating temperatures and over 30% tuning ranges were achieved. Excellent reproducibilities, good far-field patterns and reasonable linewidths (approx. 500 kHz) were found
Arthur W. Spalding: Leadership During Cultural Upheaval
\u27Leadership always occurs in the context of cultural mindsets and expectations. this article describes the work of arthur W. Spalding, who was the first family-life educator in the adventist church. Spalding was born into an era described as a “watershed” in domesticity. With the opening of the american frontier in the mid-1800s came the shift from family to individualism. Urbanization, industrialization, expanded travel, and communications eroded the social and material conditions that supported the traditional patriarchal family system. the american experience glamorized consumption, gratification, and pleasure. the fad was to reject traditional authority, particularly that of the clergy and the marriage system. ... With the radical transformation of practically every phase of life after the turn of the century, it became clear to some that something must be done to maintain the social, spiritual, and moral health of the family
A large scale prediction of bacteriocin gene blocks suggests a wide functional spectrum for bacteriocins
Bacteriocins are peptide-derived molecules produced by bacteria, whose
recently-discovered functions include virulence factors and signalling
molecules as well as their better known roles as antibiotics. To date, close to
five hundred bacteriocins have been identified and classified. Recent
discoveries have shown that bacteriocins are highly diverse and widely
distributed among bacterial species. Given the heterogeneity of bacteriocin
compounds, many tools struggle with identifying novel bacteriocins due to their
vast sequence and structural diversity. Many bacteriocins undergo
post-translational processing or modifications necessary for the biosynthesis
of the final mature form. Enzymatic modification of bacteriocins as well as
their export is achieved by proteins whose genes are often located in a
discrete gene cluster proximal to the bacteriocin precursor gene, referred to
as \textit{context genes} in this study. Although bacteriocins themselves are
structurally diverse, context genes have been shown to be largely conserved
across unrelated species. Using this knowledge, we set out to identify new
candidates for context genes which may clarify how bacteriocins are
synthesized, and identify new candidates for bacteriocins that bear no sequence
similarity to known toxins. To achieve these goals, we have developed a
software tool, Bacteriocin Operon and gene block Associator (BOA) that can
identify homologous bacteriocin associated gene clusters and predict novel
ones. We discover that several phyla have a strong preference for bactericon
genes, suggesting distinct functions for this group of molecules. Availability:
https://github.com/idoerg/BOAComment: Accepted for publication in BMC Bioinformatic
Formation of Cosmic Dust Bunnies
Planetary formation is an efficient process now thought to take place on a
relatively short astronomical time scale. Recent observations have shown that
the dust surrounding a protostar emits more efficiently at longer wavelengths
as the protoplanetary disk evolves, suggesting that the dust particles are
coagulating into fluffy aggregates, "much as dust bunnies form under a bed."
One poorly understood problem in this coagulation process is the manner in
which micron-sized, charged grains form the fractal aggregate structures now
thought to be the precursors of protoplanetary disk evolution. This study
examines the characteristics of such fractal aggregates formed by the collision
of spherical monomers and aggregates where the charge is distributed over the
aggregate structure. The aggregates are free to rotate due to collisions and
dipole-dipole electrostatic interactions. Comparisons are made for different
precursor size distributions and like-charged, oppositelycharged, and neutral
grains
The Uncertainty of Fluxes
In the ordinary quantum Maxwell theory of a free electromagnetic field,
formulated on a curved 3-manifold, we observe that magnetic and electric fluxes
cannot be simultaneously measured. This uncertainty principle reflects torsion:
fluxes modulo torsion can be simultaneously measured. We also develop the
Hamilton theory of self-dual fields, noting that they are quantized by
Pontrjagin self-dual cohomology theories and that the quantum Hilbert space is
Z/2-graded, so typically contains both bosonic and fermionic states.
Significantly, these ideas apply to the Ramond-Ramond field in string theory,
showing that its K-theory class cannot be measured.Comment: 33 pages; minor modifications for publication in Commun. Math. Phy
A latent class analysis of parental bipolar disorder: examining associations with offspring psychopathology
Bipolar disorder (BD) is highly heterogeneous, and course variations are associated with patient outcomes. This diagnostic complexity challenges identification of patients in greatest need of intervention. Additionally, course variations have implications for offspring risk. First, latent class analysis (LCA) categorized parents with BD based on salient illness characteristics: BD type, onset age, polarity of index episode, pole of majority of episodes, rapid cycling, psychosis, anxiety comorbidity, and substance dependence. Fit indices favored three parental classes with some substantively meaningful patterns. Two classes, labeled “Earlier-Onset Bipolar-I” (EO-I) and “Earlier-Onset Bipolar-II” (EO-II), comprised parents who had a mean onset age in mid-adolescence, with EO-I primarily BD-I parents and EO-II entirely BD-II parents. The third class, labeled “Later-Onset BD” (LO) had an average onset age in adulthood. Classes also varied on probability of anxiety comorbidity, substance dependence, psychosis, rapid cycling, and pole of majority of episodes. Second, we examined rates of disorders in offspring (ages 4–33, Mage=13.46) based on parental latent class membership. Differences emerged for offspring anxiety disorders only such that offspring of EO-I and EO-II parents had higher rates, compared to offspring of LO parents, particularly for daughters. Findings may enhance understanding of BD and its nosologyThis study was funded by two Brain & Behavior Research Foundation (formerly NARSAD) Independent Investigator Awards (PI: Nierenberg), a Brain & Behavior Research Foundation Young Investigator Award (PI: Henin) generously supported in part by the SHINE Initiative, and an MGH Claflin Award (PI: Henin). We thank David A. Langer, Ph.D., Thomas M. Olino, Ph.D., and Meredith Lotz Wallace, Ph.D. for their consultation. (Brain & Behavior Research Foundation; Brain & Behavior Research Foundation Young Investigator Award; SHINE Initiative; MGH Claflin Award)Accepted manuscrip
Dynamics of Diblock Copolymers in Dilute Solutions
We consider the dynamics of freely translating and rotating diblock (A-B),
Gaussian copolymers, in dilute solutions. Using the multiple scattering
technique, we have computed the diffusion and the friction coefficients D_AB
and Zeta_AB, and the change Eta_AB in the viscosity of the solution as
functions of x = N_A/N and t = l_B/l_A, where N_A, N are the number of segments
of the A block and of the whole copolymer, respectively, and l_A, l_B are the
Kuhn lengths of the A and B blocks. Specific regimes that maximize the
efficiency of separation of copolymers with distinct "t" values, have been
identified.Comment: 20 pages Revtex, 7 eps figures, needs epsf.tex and amssymb.sty,
submitted to Macromolecule
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