6,127 research outputs found
Improving Table Compression with Combinatorial Optimization
We study the problem of compressing massive tables within the
partition-training paradigm introduced by Buchsbaum et al. [SODA'00], in which
a table is partitioned by an off-line training procedure into disjoint
intervals of columns, each of which is compressed separately by a standard,
on-line compressor like gzip. We provide a new theory that unifies previous
experimental observations on partitioning and heuristic observations on column
permutation, all of which are used to improve compression rates. Based on the
theory, we devise the first on-line training algorithms for table compression,
which can be applied to individual files, not just continuously operating
sources; and also a new, off-line training algorithm, based on a link to the
asymmetric traveling salesman problem, which improves on prior work by
rearranging columns prior to partitioning. We demonstrate these results
experimentally. On various test files, the on-line algorithms provide 35-55%
improvement over gzip with negligible slowdown; the off-line reordering
provides up to 20% further improvement over partitioning alone. We also show
that a variation of the table compression problem is MAX-SNP hard.Comment: 22 pages, 2 figures, 5 tables, 23 references. Extended abstract
appears in Proc. 13th ACM-SIAM SODA, pp. 213-222, 200
Towards a bulk theory of flexoelectricity
Flexoelectricity is the linear response of polarization to a strain gradient.
Here we address the simplest class of dielectrics, namely elemental cubic
crystals, and we prove that therein there is no extrinsic (i.e. surface)
contribution to flexoelectricity in the thermodynamic limit. The flexoelectric
tensor is expressed as a bulk response of the solid, manifestly independent of
surface configurations. Furthermore, we prove that the flexoelectric responses
induced by a long-wavelength phonon and by a uniform strain gradient are
identical.Comment: 5 pages, 1 figure (2 panels
Dynamical Correlation Length and Relaxation Processes in a Glass Former
We investigate the relaxation process and the dynamical heterogeneities of
the kinetically constrained Kob--Anderson lattice glass model, and show that
these are characterized by different timescales. The dynamics is well described
within the diffusing defect paradigm, which suggest to relate the relaxation
process to a reverse--percolation transition. This allows for a geometrical
interpretation of the relaxation process, and of the different timescales
Developing Capacity, Skills, and Tobacco Control Networks to address Tobacco-related Disparities: Leadership and Advocacy Institute to Advance Minnesota’s Parity for Priority Populations (LAAMPP)
Priority populations disproportionately experience tobacco-related disparities, despite population level declines in tobacco use. The Leadership and Advocacy Institute to Advance Minnesota’s Parity for Priority Populations (LAAMPP) recruits and trains African immigrants/African Americans, Asian Americans/Pacific Islanders, American Indians, Chicano/Latinos, and LGBTQ community members to develop leaders to address tobacco harms in their communities. This paper describes and evaluates the LAAMPP Institute, and discusses lessons learned through the Institute and future directions for community-based tobacco-control efforts.
The mixed-methods evaluation included qualitative key informant interviews with LAAMPP Fellows and community and project contacts, a Skills Assessment Tool, project case studies, and a social network analysis of the Fellows’ tobacco-control social networks at baseline and follow-up.
At follow-up, Fellows’ tobacco control networks were larger, more extensive and diverse, and included more actors perceived to be influential in tobacco control. Fellows’ skills increased in core competencies (tobacco control, advocacy, facilitation, collaboration, cultural/community competence) and Fellows used tobacco, advocacy and cultural/community competencies more frequently. Four of five cohorts successfully passed policies. The results of LAAMPP suggest that a cross-cultural leadership institute contributes to the successful development of capacity and leadership skills among priority populations and may be a useful model for others working toward health equity
The use of social networking sites in eLearning
The adaptation of social networking sites within higher education has garnered significant interest in the recent years with numerous researches considering it as a possible shift from the traditional classroom based learning paradigm. Notwithstanding this increase in research and conducted studies however, the adaption of SNS based modules have failed to proliferate within Universities. This paper, commences its contribution by analyzing the various models and theories proposed in literature and amalgamates together various effective aspects for the inclusion of social technology within e-Learning. A three phased framework is further proposed which details the necessary considerations for the successful adaptation of SNS in enhancing the students learning experience. This proposal outlines the theoretical foundations which will be analyzed in practical implementation across international university campuses
Endovascular repair for acute traumatic transection of the descending thoracic aorta: experience of a single centre with a 12-years follow up
Background: Most blunt aortic injuries occur in the proximal proximal descending aorta causing acute transection
of this vessel. Generally, surgical repair of the ruptured segment of aorta is associated with high rates of morbidity
and mortality and in this view endovascular treatment seems to be a valid and safer alternative. Aim of this article
is to review our experience with endovascular approach for the treatment of acute traumatic rupture of descending
thoracic aorta.
Methods: From April 2002 to November 2014, 11 patients (9 males and 2 females) were referred to our Department
with a diagnosis of acute transection of thoracic aorta. Following preoperative Computed Tomography (CT) evaluation,
thoracic endovascular aortic repair (TEVAR) with left subclavian artery coverage was performed. Follow-up consisted
clinical and instrumental (CT, Duplex ultrasound) controls at discharge, 1, 3 and 6 months and yearly thereafter.
Results: At 12-year follow up, the overall survival for the entire patients cohort was 100 %, no major or minor
neurological complications and no episode of left arm claudication occurred. Cardiovascular, respiratory and bleeding
complications, in the early period, was represented by minor, non fatal events. No stent graft failure, collapse, leak or
distal migration were detected at CT scan during the entire follow up period.
Conclusions: According to our experience, despite the small number of patient population, TEVAR procedure with
with left subclavian artery coverage, performed in emergency settings, seems to provide excellent long term results.
Trials registration: The protocol was registered at a public trials registry, www.clinicaltrials.gov (trial identifier
NCT02376998)
Wind-sand tunnel testing of surface-mounted obstacles: Similarity requirements and a case study on a Sand Mitigation Measure
Windblown sand flow interacts with a number of surface-mounted human-built obstacles. The wind-sand flow perturbation and resulting morphodynamic response of the sand bed cannot be assessed in analytical terms. Therefore, wind-sand tunnel studies around scale physical models are often carried out. They should be driven by physical similarity theory based on dimensionless numbers referred to the whole multiphase and multiscale flow. However, similarity requirements cannot be fully satisfied under typical testing conditions and attention should be paid on the extent of the similarity relaxation. In this study, the background of wind-sand tunnel testing of surface-mounted obstacles is recalled by reviewing wind tunnel setups and similarity requirements. Then, a wind-sand tunnel campaign on a Sand Mitigation Measure is described and critically discussed. The setup dimensionless numbers are compared with statistics on those of past studies. The inescapable relaxation of similarity requirements is motivated by the test goals. The time evolution towards in-equilibrium conditions of both sand bed morphodynamics and sand transport is discussed. Finally, the results of engineering interest are described: the Sand Mitigation Measure sand trapping performance is assessed in dimensionless terms through the measurements of the incoming and outgoing sand concentration in air
Heat stress affects reproductive performance of high producing dairy cows bred in an area of southern Apennines
A 5-year retrospective (from 2008 to 2012) survey was carried out by analyzing data of high producing dairy cows reared in farms located in an area of southern Apennines. The indicators of fertility obtained were related to either season variations or the temperature-humidity index (THI). A significant lower number of conceptions evaluated per month on an annual basis (NCY), i.e., a parameter obtained by subtracting gestation length to the calving date, was found during the summer months; furthermore, this parameter decreased along with THI increase. The number of heats detected varied equally to NCY and represented the main cause of the lower fertility consequent to heat stress (HS). The age at first calving was not significantly affected by either the season or the THI. The mean number of AI/pregnancy in relation to the calving time was significantly affected by the season but it was not related to THI. The number of days open was significantly larger in the animals calved from January to July than from August to December (163±33 vs 123±36 days; P< 0.001); this causes an annual economic loss of several thousand euro in each farm analyzed. In conclusion, HS causes severe economic losses in dairy farms located in southern Apennines that are mainly due to a lower number of heats detected as well as a larger number of days open and semen doses used
Protein Crosslinks Influence Food Digestion
Enzymatic crosslinking is increasingly applied to confer specific
properties to different proteins and, consequently, to food products of
which they are components. Among the most investigated enzymes,
transglutaminases (in particular the microbial isoform, mTG) and
various oxidative biocatalysts are having special attention by food
biotechnology researchers. mTG catalyzes isopeptide bond formation
among protein molecules, leading to inter-molecular crosslinks
and being able to produce both homo- and hetero-polymers. Its
peculiar properties, such as the calcium independency, the broad
substrate specificity, the stability over a wide range of temperatures
and pH values, make such enzyme an effective tool to modify the
characteristics of many protein-based foods
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