Resolving Quantum Interference Black Box through Attosecond Photoionization Spectroscopy.

Multiphoton light-matter interactions invoke a so-called "black box" in which the experimental observations contain the quantum interference between multiple pathways. Here, we employ polarization-controlled attosecond photoelectron metrology with a partial wave manipulator to deduce the pathway interference within this quantum 'black box" for the two-photon ionization of neon atoms. The angle-dependent and attosecond time-resolved photoelectron spectra are measured across a broad energy range. Two-photon phase shifts for each partial wave are reconstructed through the comprehensive analysis of these photoelectron spectra. We resolve the quantum interference between the degenerate p→d→p and p→s→p two-photon ionization pathways, in agreement with our theoretical simulations. Our approach thus provides an attosecond time-resolved microscope to look inside the "black box" of pathway interference in ultrafast dynamics of atoms, molecules, and condensed matter.

Atomic partial wave meter by attosecond coincidence metrology.

Attosecond chronoscopy is central to the understanding of ultrafast electron dynamics in matter from gas to the condensed phase with attosecond temporal resolution. It has, however, not yet been possible to determine the timing of individual partial waves, and steering their contribution has been a substantial challenge. Here, we develop a polarization-skewed attosecond chronoscopy serving as a partial wave meter to reveal the role of each partial wave from the angle-resolved photoionization phase shifts in rare gas atoms. We steer the relative ratio between different partial waves and realize a magnetic-sublevel-resolved atomic phase shift measurement. Our experimental observations are well supported by time-dependent R-matrix numerical simulations and analytical soft-photon approximation analysis. The symmetry-resolved, partial-wave analysis identifies the transition rate and phase shift property in the attosecond photoelectron emission dynamics. Our findings provide critical insights into the ubiquitous attosecond optical timer and the underlying attosecond photoionization dynamics.

Dialogue on analytical and ab initio methods in attoscience.

The perceived dichotomy between analytical and ab initio approaches to theory in attosecond science is often seen as a source of tension and misconceptions. This Topical Review compiles the discussions held during a round-table panel at the 'Quantum Battles in Attoscience' cecam virtual workshop, to explore the sources of tension and attempt to dispel them. We survey the main theoretical tools of attoscience-covering both analytical and numerical methods-and we examine common misconceptions, including the relationship between ab initio approaches and the broader numerical methods, as well as the role of numerical methods in 'analytical' techniques. We also evaluate the relative advantages and disadvantages of analytical as well as numerical and ab initio methods, together with their role in scientific discovery, told through the case studies of two representative attosecond processes: non-sequential double ionisation and resonant high-harmonic generation. We present the discussion in the form of a dialogue between two hypothetical theoreticians, a numericist and an analytician, who introduce and challenge the broader opinions expressed in the attoscience community.

Resolving Ultrafast Spin-Orbit Dynamics in Heavy Many-Electron Atoms.

We use R-matrix with time-dependence theory, with spin-orbit effects included, to study krypton irradiated by two time-delayed extreme ultraviolet ultrashort pulses. The first pulse excites the atom to 4s^{2}4p^{5}5s. The second pulse then excites 4s4p^{6}5s autoionizing levels, whose population can be observed through their subsequent decay. By varying the time delay between the two pulses, we are able to control the excitation pathway to the autoionizing states. The use of cross-polarized light pulses allows us to isolate the two-photon pathway, with one photon taken from each pulse.

Role of prolactin in the gonadotroph responsiveness to gonadotrophin-releasing hormone during the equine annual reproductive cycle.

A combined suppressive effect of prolactin (PRL) and dopamine on the secretion of luteinising hormone (LH) at the level of the pituitary gland has been identified in sheep, a short-day breeder. However, little is known about the role of PRL in the intra-pituitary regulation of the gonadotrophic axis in long-day breeders. In the present study, we investigated the effects of PRL on LH and follicle-stimulating hormone (FSH) secretion during the equine annual reproductive cycle. Horse pituitaries were obtained during the breeding season (BS) and nonbreeding season (NBS). Cells were dispersed, plated to monolayer cultures and assigned to one of the following specific treatments: (i) medium (Control); (ii) rat PRL (rPRL); (iii) thyrotrophin-releasing hormone (TRH); (iv) bromocriptine (Br); and (v) Br + rPRL. Gonadotrophin-releasing hormone (GnRH) dose-dependently stimulated LH release during the BS and NBS. During the BS, neither rPRL nor TRH affected the LH response to GnRH, but Br significantly (P < 0.01) enhanced both basal and GnRH-stimulated LH release through a mechanism that did not involve alterations in the concentrations of PRL. However, rPRL prevented the Br-induced increase in basal and GnRH-stimulated LH output, and suppressed LH below basal values (P < 0.05). Conversely, during the NBS, no significant effects of treatments were observed. Interestingly, at this time of year, the incidence of pituitary gap junctions within the pars distalis decreased by 50% (P < 0.01). By contrast to the effects on LH, no treatment effects were detected on the FSH response to GnRH, which was only apparent during the NBS. These results reveal no direct effects of PRL but an interaction between PRL and dopamine in the inhibitory regulation of LH, but not FSH, release at the level of the pituitary in the horse, and a modulatory role of season/photoperiod associated with alterations in folliculostellate cell-derived gap junctions.

The equine hypophysis: a gland for all seasons.

The intrahypophysial mechanisms involved in the control of gonadotrophin secretion remain unclear. In the horse, a divergent pattern of gonadotrophins is observed at different stages of the reproductive cycle in response to a single secretagogue (gonadotrophin-releasing hormone), and dramatic changes in fertility take place throughout the year in response to photoperiod. This species thus provides a useful model to investigate the regulation of fertility directly at the level of the hypophysis. A series of studies were undertaken to examine the cytological arrangements and heterogeneity of gonadotrophin storage in the pars distalis (PD) and pars tuberalis (PT) of the hypophysis of male and female horses. Specifically, the seasonal and gonadal effects on distribution, density and hormonal identity of gonadotrophs, the existence of gonadotroph-lactotroph associations and the expression of prolactin receptors (PRL-R) as possible morphological bases for the differential control of gonadotrophin secretion were investigated. It became apparent that both isolated and clustered gonadotrophs are normally distributed around the pars intermedia and surrounding capillaries in the PD, and in the caudal ventral region of the PT. In the PD, no effects of season or of reproductive state on the density or number of gonadotrophs could be detected in either male or female animals. In contrast, a fivefold increase in gonadotroph density was observed in the PT during the sexually active stage. In males, robust gonadal effects were detected on the gonadotroph population; orchidectomy significantly reduced both the number and proportion of gonadotrophs, in relation to other hypophysial cell types, in both the PD and PT regions. Luteinizing hormone (LH) monohormonal, follicle-stimulating hormone (FSH) monohormonal and bihormonal gonadotrophs were identified in the PD and PT of male and female horses. Interestingly, in males, the relative proportions of gonadotroph subtypes and the LH/FSH monohormonal gonadotroph ratio were not affected by either season or the presence of the gonads. In contrast, a larger proportion of monohormonal gonadotrophs was clearly observed in sexually active females. Specific gonadotroph-lactotroph associations and expression of PRL-R in cells other than gonadotrophs were detected in the PD throughout the annual reproductive cycle. In addition to a stimulatory gonadal effect on lactotroph density, a substantial gonadal-independent effect of season was apparent on this variable. The findings have revealed important seasonal and gonadal effects on the cytological configuration of the equine hypophysis, which may provide the morphological basis for the intrahypophysial control of fertility.

Gonadotroph-lactotroph associations and expression of prolactin receptors in the equine pituitary gland throughout the seasonal reproductive cycle.

An interaction between gonadotroph and lactotroph cells of the pituitary gland has long been recognized in several species. The current study was conducted to investigate whether an association between gonadotrophs and lactotrophs occurs in mares and whether prolactin receptors are expressed within the pituitary gland of this species. The effects of both reproductive state and season on these variables were examined in pituitary glands obtained from sexually active mares in July (breeding season), sexually active mares in November (non-breeding season) and anoestrous mares in November. Pituitaries were dissected out immediately after death and immunofluorescent staining was carried out on 6 micrometer sections using specific antibodies to the LHbeta subunit, FSHbeta subunit, prolactin and prolactin receptor. Gonadotrophs were observed in both the pars distalis and pars tuberalis; although they appeared mostly as isolated cells, small groups of gonadotrophs were also identified in the pars distalis. In contrast, lactotrophs were observed only as clusters of cells exclusively in the pars distalis of sexually active and anoestrous mares in November and in most of the sexually active mares in July. A specific gonadotroph-lactotroph association was identified only between large isolated gonadotrophs and lactotroph clusters. Double immunofluorescent staining for FSHbeta and prolactin revealed a similar gonadotroph-lactotroph association to the one detected for LH gonadotrophs. No statistical difference in the gonadotroph:lactotroph ratio was observed as a result of changes in reproductive status or season. However, a tendency for a simultaneous decrease in the number of gonadotrophs and an increase in the number of lactotrophs was detected in anoestrous animals. Prolactin receptor immunoreactivity was found in the pars distalis, but not in the pars tuberalis, of sexually active (July and November) and anoestrous animals for both long and short forms of the receptor. No prolactin receptor co-localization for either form of the receptor was observed in LH or FSH gonadotrophs in either of the reproductive states examined during both summer and winter seasons. Furthermore, no significant difference was apparent in the proportion of cells expressing prolactin receptors between mares of different reproductive state or season. The specific anatomical association between gonadotroph and lactotroph cells and the expression of prolactin receptors in the equine pituitary gland indicate a potential role of prolactin in the regulation of gonadotrophin secretion. However, the absence of evidence for co-localization of prolactin receptors in LH or FSH cells does not support the hypothesis of a direct effect of prolactin on the gonadotroph as reported in a short day breeder. The results raise the possibility that, in horses, an intermediate regulatory cell may mediate the action of prolactin on gonadotroph function.

Clinical research opportunities: what you need to know for your practice.

Cardiologists and cardiovascular practitioners are facing significant reimbursement constraints. In this setting, increasing numbers of practitioners are looking to participate in clinical research as a new source of revenue. An aging population and consolidation among pharmaceutical companies, medical device companies, and contract research organizations are placing great emphasis on speed of new products to market. Opportunities exist for well-positioned and knowledgeable clinical investigators to enhance their practices, increase their professional knowledge, and expand their network of scientific colleagues. This article provides an overview of the drug and pharmaceutical industry referable to clinical investigation, the tools necessary to become a valued, principal investigator and an outline of challenges and opportunities for clinicians wishing to engage and enhance their clinical research activities.

The "big three" cardiovascular risk factors among American blacks and Hispanics.

Today's chronic diseases require "treatment" by shifting control of the outcome from the provider back to the individual and the environment in which one functions. There is a strong need to consider the individual in the context of ethnicity and culture, which express themselves in the prevalence and magnitude of risk factors, the biological impact of risk factors and expression of disease, and the potential for control of unhealthy behaviors. Educational and screening programs related to the risk factors of cigarette smoking, hypertension, and cholesterol must be structured so that recommended life-style changes are compatible with the individual's cultural values and beliefs.