1,062 research outputs found
Photovoltaic effect in ferroelectric ceramics
The ceramic structure was simulated in a form that is more tractable to correlation between experiment and theory. Single crystals (of barium titanate) were fabricated in a simple corrugated structure in which the pedestals of the corrugation simulated the grain while the intervening cuts could be filled with materials simulating the grain boundaries. The observed photovoltages were extremely small (100 mv)
Pairwise wave interactions in ideal polytropic gases
We consider the problem of resolving all pairwise interactions of shock
waves, contact waves, and rarefaction waves in 1-dimensional flow of an ideal
polytropic gas. Resolving an interaction means here to determine the types of
the three outgoing (backward, contact, and forward) waves in the Riemann
problem defined by the extreme left and right states of the two incoming waves,
together with possible vacuum formation. This problem has been considered by
several authors and turns out to be surprisingly involved. For each type of
interaction (head-on, involving a contact, or overtaking) the outcome depends
on the strengths of the incoming waves. In the case of overtaking waves the
type of the reflected wave also depends on the value of the adiabatic constant.
Our analysis provides a complete breakdown and gives the exact outcome of each
interaction.Comment: 39 page
Does Erasmus Mobility Increase Employability?:Using Register Data to Investigate the Labour Market Outcomes of University Graduates
Clustering as an example of optimizing arbitrarily chosen objective functions
This paper is a reflection upon a common practice of solving various types of learning problems by optimizing arbitrarily chosen criteria in the hope that they are well correlated with the criterion actually used for assessment of the results. This issue has been investigated using clustering as an example, hence a unified view of clustering as an optimization problem is first proposed, stemming from the belief that typical design choices in clustering, like the number of clusters or similarity measure can be, and often are suboptimal, also from the point of view of clustering quality measures later used for algorithm comparison and ranking. In order to illustrate our point we propose a generalized clustering framework and provide a proof-of-concept using standard benchmark datasets and two popular clustering methods for comparison
Reconsidering Representation Alignment for Multi-view Clustering
Aligning distributions of view representations is a core component of today's
state of the art models for deep multi-view clustering. However, we identify
several drawbacks with na\"ively aligning representation distributions. We
demonstrate that these drawbacks both lead to less separable clusters in the
representation space, and inhibit the model's ability to prioritize views.
Based on these observations, we develop a simple baseline model for deep
multi-view clustering. Our baseline model avoids representation alignment
altogether, while performing similar to, or better than, the current state of
the art. We also expand our baseline model by adding a contrastive learning
component. This introduces a selective alignment procedure that preserves the
model's ability to prioritize views. Our experiments show that the contrastive
learning component enhances the baseline model, improving on the current state
of the art by a large margin on several datasets.Comment: To appear in CVPR 2021. Code available at
https://github.com/DanielTrosten/mv
Some hydraulic properties of Sandy-silty Norweigan Tills
Norwegian tills are usually coarse. The saturated water movement is mainly concentrated along fractures, fissures and' sorted sediment zones. The studies indicate that les that 10% of the water drains through the pore system of the tillmatrix. There is no marked correlation between the grain-size composition of the till and the saturated permeability. Homogeneous Norwegian tills may form important conduits of capillary water transport from the groundwater level to the vegetation during dry summers. This is mainly because the tills are dominated by equidimensional minerals which form an open pore system and because the groundwater level in many cases is situated at shallow depths
Numerical model of the temperature dependence of the up-conversion efficiency of fluoride crystals codoped with ytterbium and thulium
We review the role of temperature on the up-conversion efficiency of materials that are good candidates to be used as the three primary-color emitters in optically written displays. A rate equation model is given for the blue emitting material that includes temperature-dependent coefficients for energy transfer and cross relaxation. Increased temperature leads to decreased up-conversion efficiency. The effect of pumping conditions on heating the emitting material is illustrated and explained. Steps to reduce the temperature rise when pumping up-conversion materials are described
Recurrent Deep Divergence-based Clustering for simultaneous feature learning and clustering of variable length time series
The task of clustering unlabeled time series and sequences entails a
particular set of challenges, namely to adequately model temporal relations and
variable sequence lengths. If these challenges are not properly handled, the
resulting clusters might be of suboptimal quality. As a key solution, we
present a joint clustering and feature learning framework for time series based
on deep learning. For a given set of time series, we train a recurrent network
to represent, or embed, each time series in a vector space such that a
divergence-based clustering loss function can discover the underlying cluster
structure in an end-to-end manner. Unlike previous approaches, our model
inherently handles multivariate time series of variable lengths and does not
require specification of a distance-measure in the input space. On a diverse
set of benchmark datasets we illustrate that our proposed Recurrent Deep
Divergence-based Clustering approach outperforms, or performs comparable to,
previous approaches
Women in senior post-graduate medicine career roles in the UK: a qualitative study
Objectives:This qualitative study sought to elicit the views, experiences, career journeys and aspirations of women in senior post-graduate medical education roles to identify steps needed to help support career progression.Design:In-depth semi-structured telephone interviews.Setting:UKParticipants:Purposive sample of 12 women in a variety of senior leadership roles in post-graduate medical education in the UK.Main outcome measures:Self reported motivating influences, factors that helped and hindered progress, key branch points, and key educational factors and social support impacting on participants' career in postgraduate medicine.Results:Respondents often reported that career journeys were serendipitous, rather than planned, formal or well structured. Senior women leaders reported having a high internal locus of control, with very high levels of commitment to the NHS. All reported significant levels of drive, although the majority indicated that they were not ambitious in the sense of a strong drive for money, prestige, recognition or power. They perceived that there was an under-representation of women in senior leadership positions and that high-quality female mentorship was particularly important in redressing this imbalance. Social support, such a spouse or other significant family member, was particularly valued as reaffirming and supporting women’s chosen career ambition. Factors that were considered to have hindered career progression included low self-confidence and self-efficacy, the so-called glass ceiling and perceived self-limiting cultural influences. Factors indirectly linked to gender such as part-time versus working full time were reportedly influential in being overlooked for senior leadership roles. Implications of these findings are discussed in the paper.Conclusion:Social support, mentorship and role modelling are all perceived as highly important in redressing perceived gender imbalances in careers in post-graduate medical education
Beta cell function after weight loss: a clinical trial comparing gastric bypass surgery and intensive lifestyle intervention
The effects of various weight loss strategies on pancreatic beta cell function remain unclear. We aimed to compare the effect of intensive lifestyle intervention (ILI) and Roux-en-Y gastric bypass surgery (RYGB) on beta cell function. Design One year controlled clinical trial (ClinicalTrials.gov identifier NCT00273104). One hundred and nineteen morbidly obese participants without known diabetes from the MOBIL study (mean (s.d.) age 43.6 (10.8) years, body mass index (BMI) 45.5 (5.6) kg/m2, 84 women) were allocated to RYGB (n=64) or ILI (n=55). The patients underwent repeated oral glucose tolerance tests (OGTTs) and were categorised as having either normal (NGT) or abnormal glucose tolerance (AGT). Twenty-nine normal-weight subjects with NGT (age 42.6 (8.7) years, BMI 22.6 (1.5) kg/m2, 19 women) served as controls. OGTT-based indices of beta cell function were calculated. One year weight reduction was 30 % (8) after RYGB and 9 % (10) after ILI (P<0.001). Disposition index (DI) increased in all treatment groups (all P<0.05), although more in the surgery groups (both P<0.001). Stimulated proinsulin-to-insulin (PI/I) ratio decreased in both surgery groups (both P<0.001), but to a greater extent in the surgery group with AGT at baseline (P<0.001). Post surgery, patients with NGT at baseline had higher DI and lower stimulated PI/I ratio than controls (both P<0.027). Gastric bypass surgery improved beta cell function to a significantly greater extent than ILI. Supra-physiological insulin secretion and proinsulin processing may indicate excessive beta cell function after gastric bypass surgery
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