Universal quantum computation by discontinuous quantum walk

Quantum walks are the quantum-mechanical analog of random walks, in which a quantum `walker' evolves between initial and final states by traversing the edges of a graph, either in discrete steps from node to node or via continuous evolution under the Hamiltonian furnished by the adjacency matrix of the graph. We present a hybrid scheme for universal quantum computation in which a quantum walker takes discrete steps of continuous evolution. This `discontinuous' quantum walk employs perfect quantum state transfer between two nodes of specific subgraphs chosen to implement a universal gate set, thereby ensuring unitary evolution without requiring the introduction of an ancillary coin space. The run time is linear in the number of simulated qubits and gates. The scheme allows multiple runs of the algorithm to be executed almost simultaneously by starting walkers one timestep apart.Comment: 7 pages, revte

Facilitators for retaining men who have sex with men in pre-exposure prophylaxis care in real world clinic settings within the United States

BACKGROUND: Pre-exposure prophylaxis (PrEP) can significantly reduce HIV acquisition especially among communities with high HIV prevalence, including men who have sex with men (MSM). Much research has been finding suboptimal PrEP persistence; however, few studies examine factors that enhance PrEP persistence in real-world settings. METHODS: We interviewed 33 patients who identified as MSM at three different PrEP clinics in three regions of the U.S. (Northeast, South, Midwest). Participants were eligible if they took PrEP and had been retained in care for a minimum of 6 months. Interviews explored social, structural, clinic-level and behavioral factors that influencing PrEP persistence. RESULTS: Through thematic analysis we identified the following factors as promoting PrEP persistence: (1) navigation to reduce out-of-pocket costs of PrEP (structural), (2) social norms that support PrEP use (social), (3) access to LGBTQ + affirming medical providers (clinical), (4) medication as part of a daily routine (behavioral), and (5) facilitation of sexual health agency (belief). DISCUSSION: In this sample, persistence in PrEP care was associated with structural and social supports as well as a high level of perceived internal control over protecting their health by taking PrEP. Patients might benefit from increased access, LGBTQ + affirming medical providers, and communications that emphasize PrEP can promote sexual health

Perspectives on long-acting formulations of pre-exposure prophylaxis (PrEP) among men who have sex with men who are non-adherent to daily oral PrEP in the United States

INTRODUCTION: Pre-exposure prophylaxis (PrEP) persistence among men who have sex with men (MSM) in real world clinical settings for HIV prevention is suboptimal. New longer-acting formulations of PrEP are becoming available, including injectables, subdermal implants, and other oral medications. These longer-acting formulations have the potential to improve retention among those who have challenges remaining adherent to daily oral PrEP. METHODS: We interviewed 49 MSM who had initiated but discontinued oral PrEP at three diverse clinics across the United States. We examined participants\u27 perspectives about long-acting PrEP formulations and how long-acting options could affect PrEP use using thematic analysis. RESULTS: Participants were not very knowledgeable about long-acting formulations of PrEP but were open to learning about them and considering use. Participants were concerned about safety and efficacy of products given that they were still newer and/or in development. Finally, participants had clear preferences for oral pills, injectables, and then subdermal implants and were most interested in options that reduced the number of visits to the clinic. CONCLUSION: Long-acting formulations of PrEP are acceptable to MSM with suboptimal PrEP persistence and have the potential to improve PrEP persistence. However, many felt they needed more information on safety, efficacy, and use to consider these options. As these long-acting formulations are implemented, public health campaigns and clinical interventions to encourage may maximize uptake particularly among those who are not currently adherent to daily oral PrEP

Sharks of the order Carcharhiniformes from the British Coniacian, Santonian and Campanian (Upper Cretaceous).

Bulk sampling of phosphate-rich horizons within the British Coniacian to Campanian (Upper Cretaceous) yielded very large samples of shark and ray teeth. All of these samples yielded teeth of diverse members of the Carcharhiniformes, which commonly dominate the fauna. The following species are recorded and described: Pseudoscyliorhinus reussi (Herman, 1977) comb. nov., Crassescyliorhinus germanicus (Herman, 1982) gen. nov., Scyliorhinus elongatus (Davis, 1887), Scyliorhinus brumarivulensis sp. nov., ? Palaeoscyllium sp., Prohaploblepharus riegrafi (Müller, 1989) gen. nov., ? Cretascyliorhinus sp., Scyliorhinidae inc. sedis 1, Scyliorhinidae inc. sedis 2, Pteroscyllium hermani sp. nov., Protoscyliorhinus sp., Leptocharias cretaceus sp. nov., Palaeogaleus havreensis Herman, 1977, Paratriakis subserratus sp. nov., Paratriakis tenuis sp. nov., Paratriakis sp. indet. and ? Loxodon sp. Taxa belonging to the families ?Proscylliidae, Leptochariidae, and Carcharhinidae are described from the Cretaceous for the first time. The evolutionary and palaeoecological implications of these newly recognised faunas are discussed

Two-photon state selection and angular momentum polarization probed by velocity map imaging: Application to H atom photofragment angular distributions from the photodissociation of two-photon state selected HCl and HBr

A formalism for calculating the angular momentum polarization of an atom or a molecule following two-photon excitation of a J-selected state is presented. This formalism is used to interpret the H atom photofragment angular distributions from single-photon dissociation of two-photon rovibronically state selected HCl and HBr prepared via a Q-branch transition. By comparison of the angular distributions measured using the velocity map imaging technique with the theoretical model it is shown that single-photon dissociation of two-photon prepared states can be used for pathway identification, allowing for the identification of the virtual state symmetry in the two-photon absorption and/or the symmetry of the dissociative state. It is also shown that under conditions of excitation with circularly polarized light, or for excitation via non-Q-branch transitions with linearly polarized light the angular momentum polarization is independent of the dynamics of the two-photon transition and analytically computable.©2004 American Institute of Physics

Larval dispersal in a changing ocean with an emphasis on upwelling regions

Dispersal of benthic species in the sea is mediated primarily through small, vulnerable larvae that must survive minutes to months as members of the plankton community while being transported by strong, dynamic currents. As climate change alters ocean conditions, the dispersal of these larvae will be affected, with pervasive ecological and evolutionary consequences. We review the impacts of oceanic changes on larval transport, physiology, and behavior. We then discuss the implications for population connectivity and recruitment and evaluate life history strategies that will affect susceptibility to the effects of climate change on their dispersal patterns, with implications for understanding selective regimes in a future ocean. We find that physical oceanographic changes will impact dispersal by transporting larvae in different directions or inhibiting their movements while changing environmental factors, such as temperature, pH, salinity, oxygen, ultraviolet radiation, and turbidity, will affect the survival of larvae and alter their behavior. Reduced dispersal distance may make local adaptation more likely in well-connected populations with high genetic variation while reduced dispersal success will lower recruitment with implications for fishery stocks. Increased dispersal may spur adaptation by increasing genetic diversity among previously disconnected populations as well as increasing the likelihood of range expansions. We hypothesize that species with planktotrophic (feeding), calcifying, or weakly swimming larvae with specialized adult habitats will be most affected by climate change. We also propose that the adaptive value of retentive larval behaviors may decrease where transport trajectories follow changing climate envelopes and increase where transport trajectories drive larvae toward increasingly unsuitable conditions. Our holistic framework, combined with knowledge of regional ocean conditions and larval traits, can be used to produce powerful predictions of expected impacts on larval dispersal as well as the consequences for connectivity, range expansion, or recruitment. Based on our findings, we recommend that future studies take a holistic view of dispersal incorporating biological and oceanographic impacts of climate change rather than solely focusing on oceanography or physiology. Genetic and paleontological techniques can be used to examine evolutionary impacts of altered dispersal in a future ocean, while museum collections and expedition records can inform modern-day range shifts