1,449 research outputs found
Exploration of Marine Resources by Photographic Remote Sensing
The interpretation of photographs in oceanographic remote sensing is discussed. The photographs were made from spacecraft with two exceptions. Two photographs were made from aircraft. There were three types of film used to make the photographs: black-and-white, color, and color IR. Black and white photography is well known; it presents pictures in various shades of gray from black to white. Color film presents pictures in color, very nearly as the human eye sees them. Color IR film presents pictures in color also but not as seen by the human eye. Blue becomes much deeper blue, green is suppressed to some extent, and red is recorded beyond the visual range of the human eye, out in the near infrared. The most noticeable effect of the use of color IR film is that leaf materials which are highly reflective in the infrared part of the spectrum are presented as red
Sexual and marital trajectories and HIV infection among ever-married women in rural Malawi.
OBJECTIVE: To explore how sexual and marital trajectories are associated with HIV infection among ever-married women in rural Malawi. METHODS: Retrospective survey data and HIV biomarker data for 926 ever-married women interviewed in the Malawi Diffusion and Ideational Change Project were used. The associations between HIV infection and four key life course transitions considered individually (age at sexual debut, premarital sexual activity, entry into marriage and marital disruption by divorce or death) were examined. These transitions were then sequenced to construct trajectories that represent the variety of patterns in the data. The association between different trajectories and HIV prevalence was examined, controlling for potentially confounding factors such as age and region. RESULTS: Although each life course transition taken in isolation may be associated with HIV infection, their combined effect appeared to be conditional on the sequence in which they occurred. Although early sexual debut, not marrying one's first sexual partner and having a disrupted marriage each increased the likelihood of HIV infection, their risk was not additive. Women who both delayed sexual debut and did not marry their first partner are, once married, more likely to experience marital disruption and to be HIV-positive. Women who marry their first partner but who have sex at a young age, however, are also at considerable risk. CONCLUSIONS: These findings identify the potential of a life course perspective for understanding why some women become infected with HIV and others do not, as well as the differentials in HIV prevalence that originate from the sequence of sexual and marital transitions in one's life. The analysis suggests, however, the need for further data collection to permit a better examination of the mechanisms that account for variations in life course trajectories and thus in lifetime probabilities of HIV infection
Higher Security Thresholds for Quantum Key Distribution by Improved Analysis of Dark Counts
We discuss the potential of quantum key distribution (QKD) for long distance
communication by proposing a new analysis of the errors caused by dark counts.
We give sufficient conditions for a considerable improvement of the key
generation rates and the security thresholds of well-known QKD protocols such
as Bennett-Brassard 1984, Phoenix-Barnett-Chefles 2000, and the six-state
protocol. This analysis is applicable to other QKD protocols like Bennett 1992.
We examine two scenarios: a sender using a perfect single-photon source and a
sender using a Poissonian source.Comment: 6 pages, 2 figures, v2: We obtained better results by using reverse
reconciliation as suggested by Nicolas Gisi
Four-strand hamstring tendon autograft for ACL reconstruction in patients aged 50years or older
SummaryIntroductionReconstruction of the anterior cruciate ligament using a four-strand hamstring tendon autograft in symptomatic patients aged 50years or older is an accepted treatment option.HypotesisFour-strand hamstring tendon autograft although not universally utilized in patients who are at least 50years old is an efficient procedure to control knee instability.Material and methodsIn this retrospective, we analyzed the clinical outcomes of 18patients treated from September 1998 to September 2003. Criteria for inclusion were the following: age above 50years at surgery, chronic anterior laxity associated or not with meniscal damage; one or more episodes of knee instability and no prior ligament surgery on the involved knee. A same operative technique (arthroscopic single-bundle four-strand hamstring reconstruction, blind femoral tunnel, through anteromedial portals), a same fixation type (absorbable interference screws in femur and tibia) and a same rehabilitation protocol were used for all these knees. The IKDC 93scores were determined pre- and postoperatively combined with anteroposterior and lateral views, single leg stance, 30° flexion stance, and passive Lachman test (Telos) postoperatively.ResultsAt mean 30month-follow-up (range 12â59months), there were no graft failure and no loss of extension for any of these knees. Three patients complained of hypoesthesia in the medial saphenous nerve territory and one patient experienced posterior knee pain. All patients graded their knee as normal or nearly normal, all were satisfied or very satisfied with their operation. None of the patients reported instability. The Lachman-Trillat test was noted âfirm end pointâ in 14knees and âdelayed firm end pointâ in four. The pivot-shift test was negative in 16knees and mild positive in two. The mean residual differential laxity was 3.1mm (0 to +6mm) for the passive Lachman test. At last follow-up, the overall IKDC score was 7A, 7B, 3C, and 1 D. Patients with preserved meniscus (nine patients) reported a lesser degree of pain and a better residual laxity control compared with patients who had undergone a meniscectomy.ConclusionAge over 50years is not a contraindication to select a hamstring tendon autograft for ACL reconstruction. This surgery can restore knee stability but does not modify the pain pattern in patients, who had a medial meniscectomy prior to the ACL reconstruction.Level of evidence: level IV, therapeutic study
Relating and learning with other beings, materials, and weather: multispecies assemblages at a Canadian forest school
In Canada, there has been a surge in outdoor and nature-based programming for young
children, such as forest schools, with interest heightening over the COVID-19 pandemic. While
there are many physical, cognitive, and emotional benefits associated with such outdoor
programs, it is important to remember that humans are not alone in these outdoor spaces.
Posthumanist, new materialist, and common worlds scholarship suggests broadening research to
gain fuller, less anthropocentric, perspectives on child-nature relationships, including in
educational settings. This multispecies ethnography of a forest school in Alberta, Canada had
two primary research questions: How, if at all, do children empathize with the more-than-human
world in a forest school setting? How might the forest school setting and pedagogy facilitate
childrenâs affective and embodied connections with the natural world?
Participants in the study included a group of six children and their educator as well as
birds, dogs, grass, trees, weather, landscape, snow, and sticks. Using video footage collected
through GoPro cameras worn by the children, photography, observations, interviewing, and local
natural-cultural information, a variety of multispecies encounters were documented and
analyzed. Several themes emerged: 1) Becoming-with animals; 2) Moving, learning, and intra-acting with trees and grass; 4) Experiencing weather, place, and landscape; and 5) Thinking with
materials. Four additional research questions also emerged: Which non-human species or
individuals presented themselves as research participants and partners in the research process? In
what ways did materials, landscapes, and weather invite childrenâs interactions/intra-actions?
How did nonparticipant observation and sit spot observations contribute to decentering the
children from the research process and what can be gleaned from this experience as a researcher? How was the use of wearable cameras as a data collection method align with goals to
respectfully bring in the childrenâs perspectives and to gain insight into child-nature relations? [...
Knot commensurability and the Berge conjecture
We investigate commensurability classes of hyperbolic knot complements in the
generic case of knots without hidden symmetries. We show that such knot
complements which are commensurable are cyclically commensurable, and that
there are at most hyperbolic knot complements in a cyclic commensurability
class. Moreover if two hyperbolic knots have cyclically commensurable
complements, then they are fibered with the same genus and are chiral. A
characterisation of cyclic commensurability classes of complements of periodic
knots is also given. In the non-periodic case, we reduce the characterisation
of cyclic commensurability classes to a generalization of the Berge conjecture.Comment: v3: This version is reorganized with minor errors fixed. Proposition
4.1, Corollary 4.2, and Proposition 5.8 were added. Question 7.2 was upgraded
to Theorem 7.2. 30 pages, 1 figur
A nonparametric framework for treatment effect modifier discovery in high dimensions
Heterogeneous treatment effects are driven by treatment effect modifiers,
pre-treatment covariates that modify the effect of a treatment on an outcome.
Current approaches for uncovering these variables are limited to
low-dimensional data, data with weakly correlated covariates, or data generated
according to parametric processes. We resolve these issues by developing a
framework for defining model-agnostic treatment effect modifier variable
importance parameters applicable to high-dimensional data with arbitrary
correlation structure, deriving one-step, estimating equation and targeted
maximum likelihood estimators of these parameters, and establishing these
estimators' asymptotic properties. This framework is showcased by defining
variable importance parameters for data-generating processes with continuous,
binary, and time-to-event outcomes with binary treatments, and deriving
accompanying multiply-robust and asymptotically linear estimators. Simulation
experiments demonstrate that these estimators' asymptotic guarantees are
approximately achieved in realistic sample sizes for observational and
randomized studies alike. This framework is applied to gene expression data
collected for a clinical trial assessing the effect of a monoclonal antibody
therapy on disease-free survival in breast cancer patients. Genes predicted to
have the greatest potential for treatment effect modification have previously
been linked to breast cancer. An open-source R package implementing this
methodology, unihtee, is made available on GitHub at
https://github.com/insightsengineering/unihtee
Experimental Implementation of Discrete Time Quantum Random Walk on an NMR Quantum Information Processor
We present an experimental implementation of the coined discrete time quantum
walk on a square using a three qubit liquid state nuclear magnetic resonance
(NMR) quantum information processor (QIP). Contrary to its classical
counterpart, we observe complete interference after certain steps and a
periodicity in the evolution. Complete state tomography has been performed for
each of the eight steps making a full period. The results have extremely high
fidelity with the expected states and show clearly the effects of quantum
interference in the walk. We also show and discuss the importance of choosing a
molecule with a natural Hamiltonian well suited to NMR QIP by implementing the
same algorithm on a second molecule. Finally, we show experimentally that
decoherence after each step makes the statistics of the quantum walk tend to
that of the classical random walk.Comment: revtex4, 8 pages, 6 figures, submitted to PR
Inventories and the Stockout Constraint in General Equilibrium
We study the implications of a stockout constraint in a dynamic general equilibrium model, which can explain both standard business cycle and inventory facts. Under this constraint, inventories and demand are complements in generating sales, and hence the optimal level of inventories increases in expected demand. We show that the inventory to sales ratio is both persistent and countercyclical because the cost of carrying inventories is mainly determined by the interest rate. We use this model to disentangle output and sales, by matching the key inventory moments, and find that preference and productivity shocks are equally important in the data. Finally, we assess whether improvements in inventory management can explain the Great Moderation. We find that, although improvements in inventory management can reduce the need for inventory holdings, which decreases output volatility relative to sales volatility, lower levels of inventories actually increases sales volatility. Because these two effects offset each other, a change in inventory management does not change output volatility to any great extent
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