778 research outputs found
Mononitration of durene
Reaction conditions under which the nitration of durene give predominantly, and in high yield, mononitrodurene (I), rather than dinitrodurene were found. The nitrating agent was No2+RF6-. Nitration with nitrosulfuric acid also gave mononitrodurene; however, byproducts such as 2.3.5.6-Me4C6HCH2C6H2Me3-2,4,5, were also formed. The NO2 PF6- gave an intermediate additional compound with durene. The reaction carried out with 3.6-dideuterodurene in D2O shows no isotope effect
Assumptions that imply quantum dynamics is linear
A basic linearity of quantum dynamics, that density matrices are mapped
linearly to density matrices, is proved very simply for a system that does not
interact with anything else. It is assumed that at each time the physical
quantities and states are described by the usual linear structures of quantum
mechanics. Beyond that, the proof assumes only that the dynamics does not
depend on anything outside the system but must allow the system to be described
as part of a larger system. The basic linearity is linked with previously
established results to complete a simple derivation of the linear Schrodinger
equation. For this it is assumed that density matrices are mapped one-to-one
onto density matrices. An alternative is to assume that pure states are mapped
one-to-one onto pure states and that entropy does not decrease.Comment: 10 pages. Added references. Improved discussion of equations of
motion for mean values. Expanded Introductio
Design of an N^7-Glycosylated Purine Nucleoside for Recognition of GC Base Pairs by Triple Helix Formation
Pyrimidine oligodeoxyribonucleotides bind in the major groove of DNA parallel to the purine Watson-Crick strand by formation of specific hydrogen bonds between thymine and adenine (T•AT triplet) and protonated cytosine and guanine (C+GC triplet) on the Hoogsteen face of the purine base. Alternatively, purine oligodeoxyribonucleotides bind in an antiparallel orientation relative to the purine Watson-Crick strand by formation of G•GC and A•AT triplets. The prerequisite protonation of cytosine in C+GC triplets leads to a considerable pH dependence in the binding affinity of C-containing oligodeoxyribonucleotides (Figure 1). Substitution of 5-methylcytosine (^mC) for cytosine results in increased binding affinities near physiological pH. In an attempt to eliminate the necessity for protonation, recent efforts have been directed toward the synthesis of nonnatural nucleosides which display the hydrogen bonding functionality of protonated cytosine
Free Fermionic Heterotic Model Building and Root Systems
We consider an alternative derivation of the GSO Projection in the free
fermionic construction of the weakly coupled heterotic string in terms of root
systems, as well as the interpretation of the GSO Projection in this picture.
We then present an algorithm to systematically and efficiently generate input
sets (i.e. basis vectors) in order to study Landscape statistics with minimal
computational cost. For example, the improvement at order 6 is approximately
10^{-13} over a traditional brute force approach, and improvement increases
with order. We then consider an example of statistics on a relatively simple
class of models.Comment: Standard Latex, 12 page
Distributional Borel Summability of Odd Anharmonic Oscillators
It is proved that the divergent Rayleigh-Schrodinger perturbation expansions
for the eigenvalues of any odd anharmonic oscillator are Borel summable in the
distributional sense to the resonances naturally associated with the system
The slow release of BMP-7 at a low dose accelerates dental implant healing in an osteopenic environment.
The aim of the present study was to investigate in vivo whether bone morphogenetic protein-7 (BMP-7) was able to promote and accelerate dental implant healing at a low dose in an osteopenic environment by using a delayed drug-release system. Skeletally mature Chinese goats, having physiologically osteopenic (osteoporotic-like) facial bones, served as an animal model. Dental implants were provided with a delayed-release drug-delivery system and BMP-7 was applied at three different dosages. The implants, inserted into healed extraction sockets, were removed 1, 2 and 3 weeks after surgery. Quantification of osseointegration and formation of new bone in the peri- implant space were measured histomorphometrically. Data revealed no evidence of any adverse drug effect at or near the implantation sites. After the first postoperative week, bone neoformation was minimal; after the second week, peri-implant bone formation appeared, particularly in the groups with low dosages of BMP-7. After 3 weeks, new-bone volume was the largest in the group with the lowest (near-physiological) dosage of BMP-7, also showing the highest efficacy of BMP-7. Other dosage or release modes were found to be significantly less effective. BMP-7 was highly efficacious in promoting and accelerating bone formation in the peri-implant space in a hostile osteopenic environment if released by a slow-mode mechanism over time at near physiological activities. Therefore, biological functionalisation of dental implants by a high-power osteogenic factor may improve their healing success in hostile bony environments (osteopenia, osteoporosis, bone atrophy etc.)
Heat kernel estimates and spectral properties of a pseudorelativistic operator with magnetic field
Based on the Mehler heat kernel of the Schroedinger operator for a free
electron in a constant magnetic field an estimate for the kernel of E_A is
derived, where E_A represents the kinetic energy of a Dirac electron within the
pseudorelativistic no-pair Brown-Ravenhall model. This estimate is used to
provide the bottom of the essential spectrum for the two-particle
Brown-Ravenhall operator, describing the motion of the electrons in a central
Coulomb field and a constant magnetic field, if the central charge is
restricted to Z below or equal 86
Design of an N^7-Glycosylated Purine Nucleoside for Recognition of GC Base Pairs by Triple Helix Formation
Pyrimidine oligodeoxyribonucleotides bind in the major groove of DNA parallel to the purine Watson-Crick strand by formation of specific hydrogen bonds between thymine and adenine (T•AT triplet) and protonated cytosine and guanine (C+GC triplet) on the Hoogsteen face of the purine base. Alternatively, purine oligodeoxyribonucleotides bind in an antiparallel orientation relative to the purine Watson-Crick strand by formation of G•GC and A•AT triplets. The prerequisite protonation of cytosine in C+GC triplets leads to a considerable pH dependence in the binding affinity of C-containing oligodeoxyribonucleotides (Figure 1). Substitution of 5-methylcytosine (^mC) for cytosine results in increased binding affinities near physiological pH. In an attempt to eliminate the necessity for protonation, recent efforts have been directed toward the synthesis of nonnatural nucleosides which display the hydrogen bonding functionality of protonated cytosine
Dynamics of Quantum Collapse in Energy Measurements
The influence of continuous measurements of energy with a finite accuracy is
studied in various quantum systems through a restriction of the Feynman
path-integrals around the measurement result. The method, which is equivalent
to consider an effective Schr\"odinger equation with a non-Hermitian
Hamiltonian, allows one to study the dynamics of the wavefunction collapse. A
numerical algorithm for solving the effective Schr\"odinger equation is
developed and checked in the case of a harmonic oscillator. The situations, of
physical interest, of a two-level system and of a metastable quantum-well are
then discussed. In the first case the Zeno inhibition observed in quantum
optics experiments is recovered and extended to nonresonant transitions, in the
second one we propose to observe inhibition of spontaneous decay in mesoscopic
heterostructures. In all the considered examples the effect of the continuous
measurement of energy is a freezing of the evolution of the system proportional
to the accuracy of the measurement itself.Comment: 20 pages with figures, compressed and uuencoded ps fil
Second order perturbation theory for embedded eigenvalues
We study second order perturbation theory for embedded eigenvalues of an
abstract class of self-adjoint operators. Using an extension of the Mourre
theory, under assumptions on the regularity of bound states with respect to a
conjugate operator, we prove upper semicontinuity of the point spectrum and
establish the Fermi Golden Rule criterion. Our results apply to massless
Pauli-Fierz Hamiltonians for arbitrary coupling.Comment: 30 pages, 2 figure
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