472 research outputs found
Spontaneous thermal expansion of nematic elastomers
We study the monodomain (single-crystal) nematic elastomer materials, all
side-chain siloxane polymers with the same mesogenic groups and crosslinking
density, but differing in the type of crosslinking. Increasing the proportion
of long di-functional segments of main-chain nematic polymer, acting as network
crosslinking, results in dramatic changes in the uniaxial equilibrium thermal
expansion on cooling from isotropic phase. At higher concentration of main
chains their behaviour dominates the elastomer properties. At low concentration
of main-chain material, we detect two distinct transitions at different
temperatures, one attributed to the main-chain, the other to the side-chain
component. The effective uniaxial anisotropy of nematic rubber, r(T)
proportional to the effective nematic order parameter Q(T), is given by the
average of the two components and thus reflects the two-transition nature of
thermal expansion. The experimental data is compared with the theoretical model
of ideal nematic elastomers; applications in high-amplitude thermal actuators
are discussed in the end
UV-isomerisation in nematic elastomers as a route to photo-mechanical transducer
The macroscopic shape of liquid crystalline elastomers strongly depends on
the order parameter of the mesogenic groups. This order can be manipulated if
photoisomerisable groups, e.g. containing N=N bonds, are introduced into the
material. We have explored the large photo-mechanical response of such an
azobenzene-containing nematic elastomer at different temperatures, using force
and optical birefringence measurements, and focusing on fundamental aspects of
population dynamics and the related speed and repeatability of the response.
The characteristic time of ``on'' and ``off'' regimes strongly depends on
temperature, but is generally found to be very long. We were able to verify
that the macroscopic relaxation of the elastomer is determined by the nematic
order dynamics and not, for instance, by the polymer network relaxation.Comment: Latex (EPJE class) 12 figure
Association between pruritus and serum concentrations of parathormone, calcium and phosphorus in hemodialysis patients.
Chronic renal disorders have a progressive course in most cases, and finally result in end-stage renal disease (ESRD). Hemodialysis (HD) is one of the mainstays in the treatment of these patients. Disturbance in calcium (Ca) and phosphorus (P) metabolism and alteration of serum levels of parathormone (PTH) are observed in these patients. One of the most common cutaneous manifestations in patients on HD is pruritus. The aim of this study is to evaluate the association between pruritus and serum concentrations of Ca, P and PTH in patients with chronic renal disease. This analytic, descriptive, cross-sectional study was performed on 120 patients on HD at the Fifth-Azar Hospital in Gorgan, Iran, in 2010. Information related to the patients, including age, gender, pruritus, time of pruritus and duration on dialysis, was extracted from questionnaires. Serum concentrations of intact PTH, Ca and P were measured. Data were analyzed by the chi-square test and SPSS-16 software. A P-value less than 0.05 was considered statistically significant. Among the 120 study patients, 50% were male and the mean age (±SD) was 49 ± 12.3 years. Sixty percent of the patients had pruritus, of whom 33.3% had PTH levels above the normal range. Among the 40% of the patients who did not have pruritus, 39.6% had PTH levels higher than the normal levels. The mean serum Ca and P levels were 8.44 ± 1.65 mg/dL and 5.48 ± 1.81 mg/dL, respectively. The mean (±SD) Ca-P product was 55.46 ± 47.16 and the mean PTH concentration was 274.34 ± 286.53 pg/mL. No significant association was found between pruritus and age, sex, serum PTH and P levels as well as Ca-P product. However, the association between serum Ca levels and pruritus was significant (P = 0.03). Our study showed that most patients with pruritus had serum Ca levels in the abnormal range (lower or higher), and there was no significant correlation between serum iPTH level and pruritis. Thus, good control of serum Ca levels is important to reduce pruritus in these patients
Nematic elastomers with aligned carbon nanotubes: new electromechanical actuators
We demonstrate, for the first time, the large electromechanical response in
nematic liquid crystalline elastomers filled with a very low (~0.01%)
concentration of carbon nanotubes, aligned along the nematic director at
preparation. The nanotubes create a very large effective dielectric anisotropy
of the composite. Their local field-induced torque is transmitted to the
rubber-elastic network and is registered as the exerted uniaxial stress of
order ~1kPa in response to a constant field of order ~1MV/m. We investigate the
dependence of the effect on field strength, nanotube concentration and
reproducibility under multiple field-on and -off cycles. The results indicate
the potential of the nanotube-nematic elastomer composites as electrically
driven actuators
Association of serum fetuin-A and biochemical parameters in hemodialysis patients.
Fetuin-A, a hepatic glycoprotein present in the circulation, is a potential inhibitor for systemic calcification. The main aim of this study was to evaluate the association between fetuin-A and other biochemical parameters as facilitator factors for developing atherosclerosis in hemodialysis (HD) patients. This case-control study was conducted on 44 HD patients undergoing treatment in 2012. Parathormone (i-PTH) and fetuin levels were performed by the enzyme-linked immunosorbent assay method, high-sensitivity C-reactive protein (hs-CRP) by chemiluminescence, low-density lipoprotein by direct enzymatic, calcium and albumin by colorimetric and phosphorous by ultraviolet (UV) methods. Chi-square was used for evaluating the association between variables and t-test was used for comparing the mean of the quantitative variables for the two groups. SPSS-16 software was used for data analysis and P-value less than 5% was considered as significant. Mean of serum fetuin level was 23.25 ± 4.90 ng/mL in HD patients and 32.92 ± 5.21 in the control group. Median of hs-CRP was 2.45 mg/dL in the patients and 1.00 mg/dL in the control group and i-PTH was 74.3 pg/mL in the patients and 7.30 pg/mL in the control group. The calcium-phosphorous product was 46.77 ± 14.22 mg/dL in the patient and 31.73 ± 6.48 mg/dL in the control group. A reverse significant association was found between fetuin-A and hs-CRP in this study. In this study, serum fetuin-A level in HD patients was lower than controls. Therefore, a low level of fetuin-A seems to be associated with atherosclerosis, inflammation and malnutrition
Mucocutaneous manifestations and nail changes in patients with end-stage renal disease on hemodialysis.
Mucocutaneous manifestations are common among patients on hemodialysis (HD). This study was undertaken to determine the prevalence of mucocutaneous manifestations in patients with end-stage renal disease (ESRD) who are on HD. In this cross-sectional, descriptive and analytic study conducted in 2009, 100 patients on HD at the Five Azar Hospital in Gorgan city were randomly selected. All the patients underwent detailed examination by a dermatologist to look for lesions in the skin, hair, nail and mucous membranes; if felt necessary, biopsy was obtained from the lesions. The findings were statistically analyzed using SPSS-13 software. For evaluation of normality of distribution, Kolmogorov-Smirnov was used, for quantitative variables Mann-Whitney and T-test (abnormal distribution) were used and for qualitative variables, Chi-2 and Fisher were used. In this study, P-value less than 0.05 was considered significant. Fifty-one males and 49 females were enrolled. The mean age was 49 ± 12 years. Diabetes was the most common cause of ESRD. In 95% of the patients, at least one mucocutaneous manifestation was present. Xerosis (78.3%) was the most common lesion, followed by pruritus (39.1%), lentigo (34.8%), skin discoloration (32.6%), leukonychia (32%) and thinning of the nail bed (24%). Xerosis, scaling, lentigo, folliculitis, idiopathic guttate hypopigmentation, leukonychia and half and half nail were associated with age. A significant relationship was seen between duration on dialysis and skin discoloration and leukonychia. Clubbing had a significant association with calcium-phosphorus product (Ca � P). There was a significant association between serum ferritin level and pruritus and tinea versicolor lesions. Our study shows that mucocutaneous manifestations are common among patients with ESRD. Identification of these manifestations and their association with causative factors are useful for preventing the lesions
Automating Carotid Intima-Media Thickness Video Interpretation with Convolutional Neural Networks
Cardiovascular disease (CVD) is the leading cause of mortality yet largely
preventable, but the key to prevention is to identify at-risk individuals
before adverse events. For predicting individual CVD risk, carotid intima-media
thickness (CIMT), a noninvasive ultrasound method, has proven to be valuable,
offering several advantages over CT coronary artery calcium score. However,
each CIMT examination includes several ultrasound videos, and interpreting each
of these CIMT videos involves three operations: (1) select three end-diastolic
ultrasound frames (EUF) in the video, (2) localize a region of interest (ROI)
in each selected frame, and (3) trace the lumen-intima interface and the
media-adventitia interface in each ROI to measure CIMT. These operations are
tedious, laborious, and time consuming, a serious limitation that hinders the
widespread utilization of CIMT in clinical practice. To overcome this
limitation, this paper presents a new system to automate CIMT video
interpretation. Our extensive experiments demonstrate that the suggested system
significantly outperforms the state-of-the-art methods. The superior
performance is attributable to our unified framework based on convolutional
neural networks (CNNs) coupled with our informative image representation and
effective post-processing of the CNN outputs, which are uniquely designed for
each of the above three operations.Comment: J. Y. Shin, N. Tajbakhsh, R. T. Hurst, C. B. Kendall, and J. Liang.
Automating carotid intima-media thickness video interpretation with
convolutional neural networks. CVPR 2016, pp 2526-2535; N. Tajbakhsh, J. Y.
Shin, R. T. Hurst, C. B. Kendall, and J. Liang. Automatic interpretation of
CIMT videos using convolutional neural networks. Deep Learning for Medical
Image Analysis, Academic Press, 201
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