1,101 research outputs found
Multistep tandem mass spectrometry for sequencing cyclic peptides in an ion-trap mass spectrometer
AbstractCollisionally activated decomposition (CAD) of a protonated cyclic peptide produces a superposition spectrum consisting of fragments produced following random ring opening of the cyclic peptide to give a set of acylium ions (or isomeric equivalents) of the same m/z. Assignment of the correct sequence is often difficult owing to lack of selectivity in the ring opening. A method is presented that utilizes multiple stages of CAD experiments in an electrospray ion-trap mass spectrometer to sequence cyclic peptides. A primary acylium ion is selected from the primary product-ion spectrum and subjected to several stages of CAD. Amino-acid residues are sequentially removed, one at each stage of the CAD, from the C-terminus, until a b2 ion is reached. Results are presented for seven cyclic peptides, ranging in sizes from four to eight amino-acid residues. This method of sequencing cyclic peptides eliminates ambiguities encountered with other MS/MS approaches. The power of the strategy lies in the capability to execute several stages of CAD upon a precursor ion and its decomposition products, allowing the cyclic peptide to be sequenced in an unambiguous, stepwise manner
High Spin Gauge Fields and Two-Time Physics
All possible interactions of a point particle with background
electromagnetic, gravitational and higher-spin fields is considered in the
two-time physics worldline formalism in (d,2) dimensions. This system has a
counterpart in a recent formulation of two-time physics in non-commutative
field theory with local Sp(2) symmetry. In either the worldline or field theory
formulation, a general Sp(2) algebraic constraint governs the interactions, and
determines equations that the background fields of any spin must obey. The
constraints are solved in the classical worldline formalism (h-bar=0 limit) as
well as in the field theory formalism (all powers of h-bar). The solution in
both cases coincide for a certain 2T to 1T holographic image which describes a
relativistic particle interacting with background fields of any spin in (d-1,1)
dimensions. Two disconnected branches of solutions exist, which seem to have a
correspondence as massless states in string theory, one containing low spins in
the zero Regge slope limit, and the other containing high spins in the infinite
Regge slope limit.Comment: LaTeX 22 pages. Typos corrected in version
An Internet-Based Simulation Model for Nitrogen Management in Agricultural Settings
Complex chemical, physical, and biological processes mediate nitrogen (N) transformations and movement during agricultural production, making the optimization of fertilizer use and environmental protection exceedingly difficult. Various computer models have been developed to simulate the site-specific fate and transport of N resulting from different crop production scenarios, but these models are very complex and difficult to use for most farmers, consultants, and conservationists. In an effort to facilitate access and simplify the use of sophisticated models, the U.S. Department of Agriculture (USDA) has developed an Internet-based nitrogen analysis tool. Based on the Nitrate Leaching and Economic Analysis Package (NLEAP), the Web site allows a user to conduct multiyear N simulation modeling specific to a crop field. Servers handle much of the required data assembly and formatting, thus sparing the user�s resources. Model runs are executed on the servers and the results are transmitted to the user. This new tool is presented along with early implementation results
Interacting Open Wilson Lines in Noncommutative Field Theories
In noncommutative field theories, it was known that one-loop effective action
describes propagation of non-interacting open Wilson lines, obeying the flying
dipole's relation. We show that two-loop effective action describes cubic
interaction among `closed string' states created by open Wilson lines. Taking
d-dimensional noncommutative [\Phi^3] theory as the simplest setup, we compute
nonplanar contribution at low-energy and large noncommutativity limit. We find
that the contribution is expressible in a remarkably simple cubic interaction
involving scalar open Wilson lines only and nothing else. We show that the
interaction is purely geometrical and noncommutative in nature, depending only
on sizes of each open Wilson line.Comment: v1: 27 pages, Latex, 7 .eps figures v2: minor wording change +
reference adde
Twisting K3 x T^2 Orbifolds
We construct a class of geometric twists of Calabi-Yau manifolds of
Voisin-Borcea type (K3 x T^2)/Z_2 and study the superpotential in a type IIA
orientifold based on this geometry. The twists modify the direct product by
fibering the K3 over T^2 while preserving the Z_2 involution. As an important
application, the Voisin-Borcea class contains T^6/(Z_2 x Z_2), the usual
setting for intersecting D6 brane model building. Past work in this context
considered only those twists inherited from T^6, but our work extends these
twists to a subset of the blow-up modes. Our work naturally generalizes to
arbitrary K3 fibered Calabi-Yau manifolds and to nongeometric constructions.Comment: 57 pages, 4 figures; uses harvmac.tex, amssym.tex; v3: minor
corrections, references adde
d-Methionine protects against cisplatin-induced neurotoxicity in cortical networks
Article discussing D-Methionine protecting against cisplatin-induced neurotoxicity in cortical networks
Decay Properties of the Connectivity for Mixed Long Range Percolation Models on
In this short note we consider mixed short-long range independent bond
percolation models on . Let be the probability that the edge
will be open. Allowing a -dependent length scale and using a
multi-scale analysis due to Aizenman and Newman, we show that the long distance
behavior of the connectivity is governed by the probability
. The result holds up to the critical point.Comment: 6 page
Towards mirror symmetry \`a la SYZ for generalized Calabi-Yau manifolds
Fibrations of flux backgrounds by supersymmetric cycles are investigated. For
an internal six-manifold M with static SU(2) structure and mirror \hat{M}, it
is argued that the product M x \hat{M} is doubly fibered by supersymmetric
three-tori, with both sets of fibers transverse to M and \hat{M}. The mirror
map is then realized by T-dualizing the fibers. Mirror-symmetric properties of
the fluxes, both geometric and non-geometric, are shown to agree with previous
conjectures based on the requirement of mirror symmetry for Killing
prepotentials. The fibers are conjectured to be destabilized by fluxes on
generic SU(3)xSU(3) backgrounds, though they may survive at type-jumping
points. T-dualizing the surviving fibers ensures the exchange of pure spinors
under mirror symmetry.Comment: 30 pages, 3 figures, LaTeX; v2: references adde
Dynamical Chiral Symmetry Breaking on the Light Front.II. The Nambu--Jona-Lasinio Model
An investigation of dynamical chiral symmetry breaking on the light front is
made in the Nambu--Jona-Lasinio model with one flavor and N colors. Analysis of
the model suffers from extraordinary complexity due to the existence of a
"fermionic constraint," i.e., a constraint equation for the bad spinor
component. However, to solve this constraint is of special importance. In
classical theory, we can exactly solve it and then explicitly check the
property of ``light-front chiral transformation.'' In quantum theory, we
introduce a bilocal formulation to solve the fermionic constraint by the 1/N
expansion. Systematic 1/N expansion of the fermion bilocal operator is realized
by the boson expansion method. The leading (bilocal) fermionic constraint
becomes a gap equation for a chiral condensate and thus if we choose a
nontrivial solution of the gap equation, we are in the broken phase. As a
result of the nonzero chiral condensate, we find unusual chiral transformation
of fields and nonvanishing of the light-front chiral charge. A leading order
eigenvalue equation for a single bosonic state is equivalent to a leading order
fermion-antifermion bound-state equation. We analytically solve it for scalar
and pseudoscalar mesons and obtain their light-cone wavefunctions and masses.
All of the results are entirely consistent with those of our previous analysis
on the chiral Yukawa model.Comment: 23 pages, REVTEX, the version to be published in Phys.Rev.D; Some
clarifications in discussion of the LC wavefunctions adde
Path-Integral bosonization of a non-local interaction and its application to the study of 1-d many-body systems
We extend the path-integral approach to bosonization to the case in which the
fermionic interaction is non-local. In particular we obtain a completely
bosonized version of a Thirring-like model with currents coupled by general
(symmetric) bilocal potentials. The model contains the Tomonaga-Luttinger model
as a special case; exploiting this fact we study the basic properties of the
1-d spinless fermionic gas: fermionic correlators, the spectrum of collective
modes, etc. Finally we discuss the generalization of our procedure to the
non-Abelian case, thus providing a new tool to be used in the study of 1-d
many-body systems with spin-flipping interactions.Comment: 26 pages LATEX, La Plata 94-0
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