46,477 research outputs found
Some properties of the dissipative model of strain-gradient plasticity
A theoretical and computational investigation is carried out of a dissipative
model of rate-independent strain-gradient plasticity and its regularization. It
is shown that the flow relation, when expressed in terms of the Cauchy stress,
is necessarily global. The most convenient approach to formulating the flow
relation is through the use of a dissipation function. It is shown, however,
that the task of obtaining the dual version, in the form of a normality
relation, is a complex one. A numerical investigation casts further light on
the response using the dissipative theory in situations of non-proportional
loading. The elastic gap, a feature reported in recent investigations, is
observed in situations in which passivation has been imposed. It is shown
computationally that the gap may be regarded as an efficient path between a
load-deformation response corresponding to micro-free boundary conditions, and
that corresponding to micro-hard boundary conditions, in which plastic strains
are set equal to zero.Comment: 26 pages, 10 figure
Habitat width along a latitudinal gradient
We use the Chowdhury ecosystem model, one of the most complex agent-based
ecological models, to test the latitude-niche breadth hypothesis, with regard
to habitat width, i.e., whether tropical species generally have narrower
habitats than high latitude ones. Application of the model has given realistic
results in previous studies on latitudinal gradients in species diversity and
Rapoport's rule. Here we show that tropical species with sufficient vagility
and time to spread into adjacent habitats, tend to have wider habitats than
high latitude ones, contradicting the latitude-niche breadth hypothesis.Comment: 13 pages including all figures, draft for a biology journa
Early assessment of vestibular function after unilateral cochlear implant surgery
Introduction : Cochlear implantation (CI) has been reported to negatively effect on the vestibular function. The study of the vestibular function has variably been conducted by different types of diagnostic tools. The combined use of modern, rapidly performable diagnostic tools could reveal useful for standardizing the evaluation protocol.
Methods: In a group of 28 subjects undergoing CI, the video Head Impulse Test (vHIT), the cervical Vestibular Evoked Myogenic Potentials (cVEMPS) and the short-form of Dizziness Handicap Inventory (DHI) questionnaire were investigated pre-operatively and post-operatively (implant on and off) in both the implanted and the contralateral, non-implanted ear. All surgeries were performed with a round window approach (RWA), except for three otosclerosis cases were the extended RWA (eRWA) was used.
Results: The vHIT of the lateral semicircular canal showed a pre-operative vestibular involvement in nearly 50% of the cases, whilst the three canals were contemporarily affected in only 14% of them. In all the hypo-functional subjects, cVEMPs were absent. A low VOR gain in all the investigated SSCC was found in 4 subjects (14%). In those subjects, (21.7%) in whom cVEMPs were pre-operatively present and normal in the operated side, absence of response was post-operatives recorded.
Discussion/Conclusion: The vestibular protocol applied for the study showed to be appropriate for distinguishing between the CI operated and the non-operated ear. In this regard, cVEMPs showed to be more sensitive than vHIT for revealing a vestibular sufferance after CI, although without statistical significance. Finally, the use of the RWA surgery was apparently not avoiding signs of vestibular impairment to occur
Domain and Geometry Agnostic CNNs for Left Atrium Segmentation in 3D Ultrasound
Segmentation of the left atrium and deriving its size can help to predict and
detect various cardiovascular conditions. Automation of this process in 3D
Ultrasound image data is desirable, since manual delineations are
time-consuming, challenging and observer-dependent. Convolutional neural
networks have made improvements in computer vision and in medical image
analysis. They have successfully been applied to segmentation tasks and were
extended to work on volumetric data. In this paper we introduce a combined
deep-learning based approach on volumetric segmentation in Ultrasound
acquisitions with incorporation of prior knowledge about left atrial shape and
imaging device. The results show, that including a shape prior helps the domain
adaptation and the accuracy of segmentation is further increased with
adversarial learning
Piezoelectric actuators for bone mechanical stimulation: exploring the concept.
Arthroplasty is liable to cause intense changes on strain levels and distribution in the boné surrounding the implant, namely stress shielding. Several solutions have been proposed for this, namely design variations and development of controlled-stiffness implants. A new approach to this problem, with potential application to other orthopaedic problems and other medical fields, would be the development of smart implants integrating systems for bone mechanical stimulation. Ideally, the implant should presente sensing capability and the ability to maintain physiological levels of strain at the implant interface. Piezoelectric materials’ huge potential as a mean to produce direct mechanical stimulation lies on the possibility of producing stimuli at a high range of frequencies and in multiple combinations. The present in vitro and preliminary in vivo studies were a first step towards the validation of the concept
The effect of the systemic inflammatory response on plasma vitamin 25 (OH) D concentrations adjusted for albumin
<b>Aim</b><p></p>
To examine the relationship between plasma 25(OH)D, CRP and albumin concentrations in two patient cohorts.<p></p>
<b>Methods</b><p></p>
5327 patients referred for nutritional assessment and 117 patients with critical illness were examined. Plasma 25 (OH) D concentrations were measured using standard methods. Intra and between assay imprecision was <10%.<p></p>
<b>Result</b><p></p>
In the large cohort, plasma 25 (OH) D was significantly associated with CRP (rs = −0.113, p<0.001) and albumin (rs = 0.192, p<0.001). 3711 patients had CRP concentrations ≤10 mg/L; with decreasing albumin concentrations ≥35, 25–34 and <25 g/l, median concentrations of 25 (OH) D were significantly lower from 35 to 28 to 14 nmol/l (p<0.001). This decrease was significant when albumin concentrations were reduced between 25–34 g/L (p<0.001) and when albumin <25 g/L (p<0.001). 1271 patients had CRP concentrations between 11–80 mg/L; with decreasing albumin concentrations ≥35, 25–34 and <25 g/l, median concentrations of 25 (OH) D were significantly lower from 31 to 24 to 19 nmol/l (p<0.001). This decrease was significant when albumin concentration were 25–34 g/L (p<0.001) and when albumin <25 g/L (p<0.001). 345 patients had CRP concentrations >80 mg/L; with decreasing albumin concentrations ≥35, 25–34 and <25 g/l, median concentrations of 25 (OH) D were not significantly altered varying from 19 to 23 to 23 nmol/l. Similar relationships were also obtained in the cohort of patients with critical illness.<p></p>
<b>Conclusion</b><p></p>
Plasma concentrations of 25(OH) D were independently associated with both CRP and albumin and consistent with the systemic inflammatory response as a major confounding factor in determining vitamin D status.<p></p>
- …