68 research outputs found
Synchronized molecular-dynamics simulation for the thermal lubrication of a polymeric liquid between parallel plates
The Synchronized Molecular-Dynamics simulation which was recently proposed by
authors [Phys. Rev. X {\bf 4}, 041011 (2014)] is applied to the analysis of
polymer lubrication between parallel plates. The rheological properties,
conformational change of polymer chains, and temperature rise due to the
viscous heating are investigated with changing the values of thermal
conductivity of the polymeric liquid. It is found that at a small applied shear
stress on the plate, the temperature of polymeric liquid only slightly
increases in inverse proportion to the thermal conductivity and the apparent
viscosity of polymeric liquid is not much affected by changing the thermal
conductivity. However, at a large shear stress, the transitional behaviors of
the polymeric liquid occur due to the interplay of the shear deformation and
viscous heating by changing the thermal conductivity. This transition is
characterized by the Nahme-Griffith number which is defined as the ratio
of the viscous heating to the thermal conduction at a characteristic
temperature. When the Nahme-Griffith number exceeds the unity, the temperature
of polymeric liquid increases rapidly and the apparent viscosity also
exponentially decreases as the thermal conductivity decreases. The conformation
of polymer chains is stretched and aligned by the shear flow for , but
the coherent structure becomes disturbed by the thermal motion of molecules for
.Comment: 19 pages, 3 figures. arXiv admin note: substantial text overlap with
arXiv:1401.124
A Model for Hybrid Simulations of Molecular Dynamics and CFD
We propose a method for multi-scale hybrid simulations of molecular dynamics
(MD) and computational fluid dynamics (CFD). In the method, usual lattice-mesh
based simulations are applied for CFD level, but each lattice is associated
with a small MD cell which generates a "local stress" according to a "local
flow field" given from CFD instead of using any constitutive functions at CFD
level. We carried out the hybrid simulations for some elemental flow problems
of simple Lennard-Jones liquids and compared the results with those obtained by
usual CFDs with a Newtonian constitutive relation in order to examine the
validity of our hybrid simulation method. It is demonstrated that our hybrid
simulations successfully reproduced the correct flow behavior obtained from
usual CFDs as far as the mesh size and the time-step of
CFD are not too large comparing to the system size and the
sampling duration of MD simulations performed at each time step of
CFDs. Otherwise, simulations are affected by large fluctuations due to poor
statistical averages taken in the MD part. Properties of the fluctuations are
analyzed in detail.Comment: 17 pages including 9 figure
Rheology of a supercooled polymer melt near an oscillating plate: an application of multiscale modeling
The behavior of a supercooled polymer melt composed of short chains with ten
beads near an oscillating plate are simulated by using a hybrid simulation of
molecular dynamics (MD) and computational fluid dynamics (CFD). In the method,
the macroscopic dynamics are solved by using CFD, but, instead of using any
constitutive equations, a local stress is calculated by using a non-equilibrium
MD simulation associated at each lattice node in the CFD calculation. It is
seen that the local rheology of the melt varies considerably in a thin viscous
diffusion layer that arises near an oscillating plate. It is also found that
the local rheology of the melt is divided into the three different regimes,
i.e., the viscous fluid, viscoelastic liquid, and viscoelastic solid regimes,
according to the local Deborah number , which is defined with the Rouse or
relaxation time, or , and the angular frequency
of the plate as = or
=. The melt behaves as a viscous fluid when
, and the crossover between the liquid-like and solid-like
regime takes place around
Multiscale modeling and simulation for polymer melt flows between parallel plates
The flow behaviors of polymer melt composed of short chains with ten beads
between parallel plates are simulated by using a hybrid method of molecular
dynamics and computational fluid dynamics. Three problems are solved: creep
motion under a constant shear stress and its recovery motion after removing the
stress, pressure-driven flows, and the flows in rapidly oscillating plates. In
the creep/recovery problem, the delayed elastic deformation in the creep motion
and evident elastic behavior in the recovery motion are demonstrated. The
velocity profiles of the melt in pressure-driven flows are quite different from
those of Newtonian fluid due to shear thinning. Velocity gradients of the melt
become steeper near the plates and flatter at the middle between the plates as
the pressure gradient increases and the temperature decreases. In the rapidly
oscillating plates, the viscous boundary layer of the melt is much thinner than
that of Newtonian fluid due to the shear thinning of the melt. Three different
rheological regimes, i.e., the viscous fluid, visco-elastic liquid, and
visco-elastic solid regimes, form over the oscillating plate according to the
local Deborah numbers. The melt behaves as a viscous fluid in a region for
, and the crossover between the liquid-like and
solid-like regime takes place around (where
is the angular frequency of the plate and and
are Rouse and relaxation time, respectively).Comment: 13pages, 12figure
Paclitaxel-Based Chemotherapy for Advanced Pancreatic Cancer after Gemcitabine-Based Therapy Failure: A Case Series of 5 Patients
Background/Objectives: Gemcitabine (GEM) is a gold-standard chemotherapy agent for advanced pancreatic cancer. Because of the malignant character of the disease, nearly all patients show disease progression despite treatment with GEM-based chemotherapy; therefore, second-line chemotherapy may be beneficial for these patients. We report a retrospective analysis of 5 patients with advanced pancreatic cancer, treated with a paclitaxel-containing regimen as second-, third- or fourth-line chemotherapy after various therapies, such as a GEM-based regimen, S-1 regimen, and chemoradiation. We retrospectively analyzed the efficacy and adverse events, and evaluated the paclitaxel-containing regimens. A review of the literature is also discussed. Results: The median overall survival from the start of salvage therapy was 10.7 months. The disease control rate of the paclitaxel-containing regimen according to RECIST criteria was 60%, including complete response in 0 patients, partial response in 3, and stable disease in 2. Two patients had malignant ascites at the start of this salvage therapy, and in both of them the ascites and clinical complaints improved. Grade 3 and 4 hematological adverse events were observed in 2 patients and 1 patient, respectively. Conclusion: Salvage paclitaxel-based therapy could be beneficial to advanced pancreatic cancer patients who maintain good performance status after several chemotherapy failures
Resting energy expenditure depends on energy intake during weight loss in people with obesity: a retrospective cohort study
Abstract Objective: Resting energy expenditure (REE) decreases if there is reduced energy intake and body weight (BW). The decrease in REE could make it difficult for patients with obesity to maintain decreased BW. This study aimed to investigate the correlation among changes in REE, energy intake, and BW during the weight loss process in patients with obesity. Materials and methods: We conducted a retrospective cohort study of patients hospitalized for the treatment of obesity in Japan. Patients received fully controlled diet during hospitalization and performed exercises if able. REE was measured once a week using a hand-held indirect calorimetry. Energy intake was determined by actual dietary intake. Results: Of 44 inpatients with obesity, 17 were included in the analysis. Their BW decreased significantly after 1 week (−4.7 ± 2.0 kg, P < 0.001) and 2 weeks (−5.7 ± 2.2 kg, P < 0.001). The change in REE after 1 and 2 weeks was positively correlated with the energy intake/energy expenditure ratio (r = 0.66, P = 0.004 at 1 week, r = 0.71, P = 0.002 at 2 weeks). Using a regression equation (y = 0.5257x – 43.579), if the energy intake/energy expenditure ratio within the second week was 82.9%, the REE after 2 weeks was similar to the baseline level. There was no significant correlation between the change in REE and BW. Conclusions: Our data suggest that changes in REE depend on energy intake/energy expenditure ratio and that the decrease in REE can be minimized by matching energy intake to energy expenditure, even during the weight loss process
Second nationwide surveillance of bacterial pathogens in patients with acute uncomplicated cystitis conducted by Japanese Surveillance Committee from 2015 to 2016: antimicrobial susceptibility of Escherichia coli, Klebsiella pneumoniae, and Staphylococcus saprophyticus
The Japanese Surveillance Committee conducted a second nationwide surveillance of antimicrobial susceptibility patterns of uropathogens responsible for acute uncomplicated cystitis (AUC) in premenopausal patients aged 16–40 years old at 31 hospitals throughout Japan from March 2015 to February 2016. In this study, the susceptibility of causative bacteria (Escherichia coli, Klebsiella pneumoniae, Staphylococcus saprophyticus) for various antimicrobial agents was investigated by isolation and culturing of organisms obtained from urine samples. In total, 324 strains were isolated from 361 patients, including E. coli (n = 220, 67.9%), S. saprophyticus (n = 36, 11.1%), and K. pneumoniae (n = 7, 2.2%). The minimum inhibitory concentrations (MICs) of 20 antibacterial agents for these strains were determined according to the Clinical and Laboratory Standards Institute (CLSI) manual. At least 93% of the E. coli isolates showed susceptibility to fluoroquinolones and cephalosporins, whereas 100% of the S. saprophyticus isolates showed susceptibility to fluoroquinolones and aminoglycosides. The proportions of fluoroquinolone-resistant and extended-spectrum β-lactamase (ESBL)-producing E. coli strains were 6.4% (13/220) and 4.1% (9/220), respectively. The antimicrobial susceptibility of K. pneumoniae was retained during the surveillance period, while no multidrug-resistant strains were identified.
In summary, antimicrobial susceptibility results of our second nationwide surveillance did not differ significantly from those of the first surveillance. Especially the numbers of fluoroquinolone-resistant and ESBL-producing E. coli strains were not increased in premenopausal patients with AUC in Japan
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