Control of recollision wave packets for molecular orbital tomography using short laser pulses

The tomographic imaging of arbitrary molecular orbitals via high-order harmonic generation requires that electrons recollide from one direction only. Within a semi-classical model, we show that extremely short phase-stabilized laser pulses offer control over the momentum distribution of the returning electrons. By adjusting the carrier-envelope phase, recollisions can be forced to occur from mainly one side, while retaining a broad energy spectrum. The signatures of the semi-classical distributions are observed in harmonic spectra obtained by numerical solution of the time-dependent Schr\"{o}dinger equation.Comment: 8 pages, 4 figures; v2: Added some extra clarifications; v3: minor grammatical change

Microeconometric evidence on demand-side real rigidity and implications for monetary non-neutrality

To model the observed slow response of aggregate real variables to nominal shocks, most macroeconomic models incorporate real rigidities in addition to nominal rigidities. One popular way of modelling such a real rigidity is to assume a non-constant demand elasticity. By using a homescan data set for three European countries, including prices and quantities bought for a large number of goods, in addition to consumer characteristics, we provide estimates of price elasticities of demand and on the degree of demand-side real rigidities. We find that price elasticities of demand are about 4 in the median. Furthermore, we find evidence for demand-side real rigidities. These are, however, much smaller than what is often assumed in macroeconomic models. The median estimate for demand-side real rigidity, the super-elasticity, is in a range between 1 and 2. To quantitatively assess the implications of our empirical estimates, we calibrate a menu-cost model with the estimated super-elasticity. We find that the degree of monetary non-neutrality doubles in the model including demand-side real rigidity, compared to the model with only nominal rigidity, suggesting a multiplier effect of around two. However, the model can explain only up to 6% of the monetary non-neutrality observed in the data, implying that additional multipliers are necessary to match the behavior of aggregate variables

Microeconometric evidence on demand-side real rigidity and implications for monetary non-neutrality

To model the observed slow response of aggregate real variables to nominal shocks, most macroeconomic models incorporate real rigidities in addition to nominal rigidities. One popular way of modelling such a real rigidity is to assume a non-constant demand elasticity. By using a homescan data set for three European countries, including prices and quantities bought for a large number of goods, in addition to consumer characteristics, we provide estimates of price elasticities of demand and on the degree of demand-side real rigidities. We find that price elasticities of demand are about 4 in the median. Furthermore, we find evidence for demand-side real rigidities. These are, however, much smaller than what is often assumed in macroeconomic models. The median estimate for demand-side real rigidity, the super-elasticity, is in a range between 1 and 2. To quantitatively assess the implications of our empirical estimates, we calibrate a menu-cost model with the estimated super-elasticity. We find that the degree of monetary non-neutrality doubles in the model including demand-side real rigidity, compared to the model with only nominal rigidity, suggesting a multiplier effect of around two. However, the model can explain only up to 6% of the monetary non-neutrality observed in the data, implying that additional multipliers are necessary to match the behavior of aggregate variables

Intrinsic channel closing in strong-field single ionization of H2

The ionization of H2 in intense laser pulses is studied by numerical integration of the time-dependent Schr\"odinger equation for a single-active-electron model including the vibrational motion. The electron kinetic-energy spectra in high-order above-threshold ionization are strongly dependent on the vibrational quantum number of the created H2+ ion. For certain vibrational states, the electron yield in the mid-plateau region is strongly enhanced. The effect is attributed to channel closings, which were previously observed in atoms by varying the laser intensity.Comment: 11 pages, LaTeX; changed conten

PON1 status does not influence cholinesterase activity in Egyptian agricultural workers exposed to chlorpyrifos.

Animal studies have shown that paraoxonase 1 (PON1) genotype can influence susceptibility to the organophosphorus pesticide chlorpyrifos (CPF). However, Monte Carlo analysis suggests that PON1 genotype may not affect CPF-related toxicity at low exposure conditions in humans. The current study sought to determine the influence of PON1 genotype on the activity of blood cholinesterase as well as the effect of CPF exposure on serum PON1 in workers occupationally exposed to CPF. Saliva, blood and urine were collected from agricultural workers (n=120) from Egypt's Menoufia Governorate to determine PON1 genotype, blood cholinesterase activity, serum PON1 activity towards chlorpyrifos-oxon (CPOase) and paraoxon (POase), and urinary levels of the CPF metabolite 3,5,6-trichloro-2-pyridinol (TCPy). The PON1 55 (P≤0.05) but not the PON1 192 genotype had a significant effect on CPOase activity. However, both the PON1 55 (P≤0.05) and PON1 192 (P≤0.001) genotypes had a significant effect on POase activity. Workers had significantly inhibited AChE and BuChE after CPF application; however, neither CPOase activity nor POase activity was associated with ChE depression when adjusted for CPF exposure (as determined by urinary TCPy levels) and stratified by PON1 genotype. CPOase and POase activity were also generally unaffected by CPF exposure although there were alterations in activity within specific genotype groups. Together, these results suggest that workers retained the capacity to detoxify chlorpyrifos-oxon under the exposure conditions experienced by this study population regardless of PON1 genotype and activity and that effects of CPF exposure on PON1 activity are minimal

Magnitude of behavioral deficits varies with job-related chlorpyrifos exposure levels among Egyptian pesticide workers.

Chronic occupational exposure to organophosphorus pesticides (OPs) is consistently associated with deficits on behavioral tests when compared to unexposed comparison groups. However, a dose-response relationship has yet to be established, leading some to doubt an association between occupational OP exposure and behavioral deficits. Pesticide application teams in Egypt who are primarily exposed to one OP, chlorpyrifos (CPF), were recruited into a field assessment. Trail Making A and the more challenging Trail Making B tests were administered to 54 engineers (who supervise the pesticide application process, usually from the side of the field), 59 technicians (who guide the pesticide applicators in the field), 31 applicators (who mix and apply pesticides using knapsack sprayers), and 150 controls (who did not work in the fields) at two different times during the OP application season as well as immediately after applications had ended and 1.5 months later. All participants were males since only males work on pesticide application teams in Egypt. Urinary levels of 3,5,6-trichloro-2-pyridinol (TCPy), a specific metabolite of CPF, confirmed the pattern of lower to higher CPF exposures from engineers to technicians to applicators, and these were all greater than urinary metabolite levels in controls. A consistent relationship between job title and performance speed on the behavioral task was observed: Controls had the best (fastest) performance on Trail Making A and B tests throughout the application season, and applicators had significantly slower performance than engineers on Trail Making A (p = 0.015) and B (p = 0.003). However, individual urinary TCPy, blood acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) levels did not predict individual performance. This study identifies a dose-related effect based on job title, which serves as a surrogate for chronic exposure in that differing job titles exhibit varying group exposure levels. The results establish that chronic occupational exposure to chlorpyrifos is neurotoxic and suggest that the classic biomarkers of recent CPF exposure are not predictive of chronic exposure effects

Distinctive Structural and Molecular Features of Myelinated Inhibitory Axons in Human Neocortex.

Numerous types of inhibitory neurons sculpt the performance of human neocortical circuits, with each type exhibiting a constellation of subcellular phenotypic features in support of its specialized functions. Axonal myelination has been absent among the characteristics used to distinguish inhibitory neuron types; in fact, very little is known about myelinated inhibitory axons in human neocortex. Here, using array tomography to analyze samples of neurosurgically excised human neocortex, we show that inhibitory myelinated axons originate predominantly from parvalbumin-containing interneurons. Compared to myelinated excitatory axons, they have higher neurofilament and lower microtubule content, shorter nodes of Ranvier, and more myelin basic protein (MBP) in their myelin sheath. Furthermore, these inhibitory axons have more mitochondria, likely to sustain the high energy demands of parvalbumin interneurons, as well as more 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP), a protein enriched in the myelin cytoplasmic channels that are thought to facilitate the delivery of nutrients from ensheathing oligodendrocytes. Our results demonstrate that myelinated axons of parvalbumin inhibitory interneurons exhibit distinctive features that may support the specialized functions of this neuron type in human neocortical circuits

Theory of high-order harmonic generation from molecules by intense laser pulses

We show that high-order harmonics generated from molecules by intense laser pulses can be expressed as the product of a returning electron wave packet and the photo-recombination cross section (PRCS) where the electron wave packet can be obtained from simple strong-field approximation (SFA) or from a companion atomic target. Using these wave packets but replacing the PRCS obtained from SFA or from the atomic target by the accurate PRCS from molecules, the resulting HHG spectra are shown to agree well with the benchmark results from direct numerical solution of the time-dependent Schr\"odinger equation, for the case of H$_2^+$ in laser fields. The result illustrates that these powerful theoretical tools can be used for obtaining high-order harmonic spectra from molecules. More importantly, the results imply that the PRCS extracted from laser-induced HHG spectra can be used for time-resolved dynamic chemical imaging of transient molecules with temporal resolutions down to a few femtoseconds.Comment: 10 pages, 5 figure

Semi- and Non-relativistic Limit of the Dirac Dynamics with External Fields

We show how to approximate Dirac dynamics for electronic initial states by semi- and non-relativistic dynamics. To leading order, these are generated by the semi- and non-relativistic Pauli hamiltonian where the kinetic energy is related to $\sqrt{m^2 + \xi^2}$ and $\xi^2 / 2m$, respectively. Higher-order corrections can in principle be computed to any order in the small parameter v/c which is the ratio of typical speeds to the speed of light. Our results imply the dynamics for electronic and positronic states decouple to any order in v/c << 1. To decide whether to get semi- or non-relativistic effective dynamics, one needs to choose a scaling for the kinetic momentum operator. Then the effective dynamics are derived using space-adiabatic perturbation theory by Panati et. al with the novel input of a magnetic pseudodifferential calculus adapted to either the semi- or non-relativistic scaling.Comment: 42 page

LCAA, a Novel Factor Required for Magnesium Protoporphyrin Monomethylester Cyclase Accumulation and Feedback Control of Aminolevulinic Acid Biosynthesis in Tobacco

Low Chlorophyll Accumulation A (LCAA) antisense plants were obtained from a screen for genes whose partial down-regulation results in a strong chlorophyll deficiency in tobacco (Nicotiana tabacum). The LCAA mutants are affected in a plastid-localized protein of unknown function, which is conserved in cyanobacteria and all photosynthetic eukaryotes. They suffer from drastically reduced light-harvesting complex (LHC) contents, while the accumulation of all other photosynthetic complexes per leaf area is less affected. As the disturbed accumulation of LHC proteins could be either attributable to a defect in LHC biogenesis itself or to a bottleneck in chlorophyll biosynthesis, chlorophyll synthesis rates and chlorophyll synthesis intermediates were measured. LCAA antisense plants accumulate magnesium (Mg) protoporphyrin monomethylester and contain reduced protochlorophyllide levels and a reduced content of CHL27, a subunit of the Mg protoporphyrin monomethylester cyclase. Bimolecular fluorescence complementation assays confirm a direct interaction between LCAA and CHL27. 5-Aminolevulinic acid synthesis rates are increased and correlate with an increased content of glutamyl-transfer RNA reductase. We suggest that LCAA encodes an additional subunit of the Mg protoporphyrin monomethylester cyclase, is required for the stability of CHL27, and contributes to feedback-control of 5-aminolevulinic acid biosynthesis, the rate-limiting step of chlorophyll biosynthesis