267 research outputs found
Ions in Fluctuating Channels: Transistors Alive
Ion channels are proteins with a hole down the middle embedded in cell
membranes. Membranes form insulating structures and the channels through them
allow and control the movement of charged particles, spherical ions, mostly
Na+, K+, Ca++, and Cl-. Membranes contain hundreds or thousands of types of
channels, fluctuating between open conducting, and closed insulating states.
Channels control an enormous range of biological function by opening and
closing in response to specific stimuli using mechanisms that are not yet
understood in physical language. Open channels conduct current of charged
particles following laws of Brownian movement of charged spheres rather like
the laws of electrodiffusion of quasi-particles in semiconductors. Open
channels select between similar ions using a combination of electrostatic and
'crowded charge' (Lennard-Jones) forces. The specific location of atoms and the
exact atomic structure of the channel protein seems much less important than
certain properties of the structure, namely the volume accessible to ions and
the effective density of fixed and polarization charge. There is no sign of
other chemical effects like delocalization of electron orbitals between ions
and the channel protein. Channels play a role in biology as important as
transistors in computers, and they use rather similar physics to perform part
of that role. Understanding their fluctuations awaits physical insight into the
source of the variance and mathematical analysis of the coupling of the
fluctuations to the other components and forces of the system.Comment: Revised version of earlier submission, as invited, refereed, and
published by journa
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The independent association between parathyroid hormone levels and hyperuricemia: a national population study
Introduction: Increased frequencies of hyperuricemia and gout have been associated with primary hyperparathyroidism, and recent clinical trials of parathyroid hormone (PTH) have reported hyperuricemic adverse events. We evaluated the potential population impact of PTH on serum uric acid (SUA) levels by using a nationally representative sample of United States adults. Methods: By using data from 8,316 participants aged 18 years and older in the National Health and Nutrition Examination Survey 2003 to 2006, we examined the relation between serum PTH and SUA levels with weighted linear regression. Additionally, we examined the relation with hyperuricemia by using weighted logistic regression. Results: SUA levels increased with increasing serum PTH concentration. After adjusting for age, sex, dietary factors, glomerular filtration rate (GFR), and other potentially related biomarkers (calcium, phosphorus, alkaline-phosphatase, 25-hydroxyvitamin D), the SUA level differences from the bottom (referent) to top quintiles of serum PTH levels were 0, 8, 13, 14, and 19 μM (95% CI, 12 to 26; P for trend, < 0.001). These estimates were larger among renally impaired individuals (multivariate SUA difference between the extreme quintiles of PTH, 26 versus 15 μM among those with GFR ≥ 60 versus < 60 ml/min per 1.73 m2, respectively) (P for interaction = 0.004). The odds of hyperuricemia by various definitions increased with increasing PTH levels as well (multivariate P values for trend, < 0.05). Conclusions: These nationally representative data indicate that serum PTH levels are independently associated with serum uric acid levels and the frequency of hyperuricemia at the population level
Is it possible to formulate least action principle for dissipative systems?
A longstanding open question in classical mechanics is to formulate the least
action principle for dissipative systems. In this work, we give a general
formulation of this principle by considering a whole conservative system
including the damped moving body and its environment receiving the dissipated
energy. This composite system has the conservative Hamiltonian
where is the kinetic energy of the moving body, its potential
energy and the energy of the environment. The Lagrangian can be derived
by using the usual Legendre transformation where is the
total kinetic energy of the environment. An equivalent expression of this
Lagrangian is where is the energy dissipated by the
friction from the moving body into the environment from the beginning of the
motion. The usual variation calculus of least action leads to the correct
equation of the damped motion. We also show that this general formulation is a
natural consequence of the virtual work principle.Comment: 11 pages, no figur
Relapsed acute myeloid leukemia presenting as conjunctival myeloid sarcoma: a case report
Abstract
Background
Conjunctival myeloid sarcoma (MS) as an isolated presentation of acute myeloid leukemia (AML) relapse is rare. Here, we report a case of unilateral conjunctival MS revealed as a sign of AML relapse.
Case presentation
A 50-year-old man with a history of AML in remission visited our clinic presenting with a left conjunctival injection persisting for 1 month. Diffuse subconjunctival thickening with conjunctival vascular engorgement was observed. Ultrasound biomicroscopy revealed a hyper-reflective, thickened conjunctiva in his left eye. During the incisional biopsy, the lesion was strongly attached to the underlying sclera; histopathologic examination revealed infiltration of leukemic blasts. The relapse of AML was confirmed by a successive bone marrow biopsy. The ocular lesion disappeared after allogeneic peripheral blood stem cell transplantation (PBSCT) and concomitant salvage radiotherapy on the left eye. The patient has remained in remission for 3 years after allogeneic PBSCT.
Conclusions
Incidental conjunctival lesions can indicate AML relapse in patients treated earlier for AML. An ophthalmologist may have a role in the early detection of AML when a patient presents with an atypical conjunctival lesion
Visual outcomes and safety after bilateral implantation of a trifocal presbyopia correcting intraocular lens in a Korean population: a prospective single-arm study
Abstract
Background
To investigate the 3-month postoperative performance and safety after implantation of a trifocal intraocular lens (IOL) in a Korean population.
Methods
This was a clinical, prospective, multicenter, single-arm study. Forty-four subjects (88 eyes) with bilateral cataract with expected postoperative corneal astigmatism of < 1.00 diopter (D) and no ocular disease or eye condition underwent bilateral implantation of the AcrySof IQ® PanOptix IOL (TFNT00). Postoperative examination at 3 months included binocular defocus curve; binocular best corrected distance visual acuity (BCDVA); monocular/binocular uncorrected VA (UCVA) at distance (4 m), intermediate (60 cm), and near (40 cm); contrast sensitivity under photopic conditions with/without glare; and subjective outcomes, including satisfaction and spectacle independence.
Results
Binocular defocus curve at 3 months after bilateral implantation showed VA of 0.1 logMAR or better from + 0.5 D through − 2.5 D. Binocular BCDVA mean ± SD at 4 m was − 0.05 ± 0.07 logMAR. Binocular and monocular UCVA was 0.03 ± 0.1 and 0.08 ± 0.12 logMAR (4 m), − 0.00 ± 0.11 and 0.05 ± 0.13 logMAR (60 cm), and 0.03 ± 0.12 and 0.09 ± 0.13 logMAR (40 cm), respectively. Contrast sensitivity with glare was 1.67 ± 0.13, 1.91 ± 0.17, 1.54 ± 0.21, and 1.14 ± 0.20 log units at 3, 6, 12, and 18 cycles/degree, respectively. At near and intermediate distances, 84 and 77% of subjects reported good/excellent satisfaction, and 84 and 91% of subjects reported spectacle independence, respectively.
Conclusions
In a Korean population, visual performance of the trifocal TFNT00 IOL 3 months postoperatively was < 0.1 logMAR for binocular UCVA at all distances, with high subject satisfaction and spectacle independence.
Trial registration
www.ClinicalTrials.gov (
NCT03268746
). Registered August 31, 2017
On the General Ericksen-Leslie System: Parodi's Relation, Well-posedness and Stability
In this paper we investigate the role of Parodi's relation in the
well-posedness and stability of the general Ericksen-Leslie system modeling
nematic liquid crystal flows. First, we give a formal physical derivation of
the Ericksen-Leslie system through an appropriate energy variational approach
under Parodi's relation, in which we can distinguish the
conservative/dissipative parts of the induced elastic stress. Next, we prove
global well-posedness and long-time behavior of the Ericksen-Leslie system
under the assumption that the viscosity is sufficiently large. Finally,
under Parodi's relation, we show the global well-posedness and Lyapunov
stability for the Ericksen-Leslie system near local energy minimizers. The
connection between Parodi's relation and linear stability of the
Ericksen-Leslie system is also discussed
Oscillatory surface rheotaxis of swimming E. coli bacteria
Bacterial contamination of biological conducts, catheters or water resources
is a major threat to public health and can be amplified by the ability of
bacteria to swim upstream. The mechanisms of this rheotaxis, the reorientation
with respect to flow gradients, often in complex and confined environments, are
still poorly understood. Here, we follow individual E. coli bacteria swimming
at surfaces under shear flow with two complementary experimental assays, based
on 3D Lagrangian tracking and fluorescent flagellar labelling and we develop a
theoretical model for their rheotactic motion. Three transitions are identified
with increasing shear rate: Above a first critical shear rate, bacteria shift
to swimming upstream. After a second threshold, we report the discovery of an
oscillatory rheotaxis. Beyond a third transition, we further observe
coexistence of rheotaxis along the positive and negative vorticity directions.
A full theoretical analysis explains these regimes and predicts the
corresponding critical shear rates. The predicted transitions as well as the
oscillation dynamics are in good agreement with experimental observations. Our
results shed new light on bacterial transport and reveal new strategies for
contamination prevention.Comment: 12 pages, 5 figure
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Fried food consumption, genetic risk, and body mass index: gene-diet interaction analysis in three US cohort studies
Objective: To examine the interactions between genetic predisposition and consumption of fried food in relation to body mass index (BMI) and obesity. Design: Prospective cohort study. Setting: Health professionals in the United States. Participants: 9623 women from the Nurses’ Health Study, 6379 men from the Health Professionals Follow-up Study, and a replication cohort of 21 421 women from the Women’s Genome Health Study. Main outcome measure Repeated measurement of BMI over follow-up. Results: There was an interaction between fried food consumption and a genetic risk score based on 32 BMI-associated variants on BMI in both the Nurses’ Health Study and Health Professionals Follow-up Study (P≤0.001 for interaction). Among participants in the highest third of the genetic risk score, the differences in BMI between individuals who consumed fried foods four or more times a week and those who consumed fried foods less than once a week amounted to 1.0 (SE 0.2) in women and 0.7 (SE 0.2) in men, whereas the corresponding differences were 0.5 (SE 0.2) and 0.4 (SE 0.2) in the lowest third of the genetic risk score. The gene-diet interaction was replicated in the Women’s Genome Health Study (P<0.001 for interaction). Viewed differently, the genetic association with adiposity was strengthened with higher consumption of fried foods. In the combined three cohorts, the differences in BMI per 10 risk alleles were 1.1 (SE 0.2), 1.6 (SE 0.3), and 2.2 (SE 0.6) for fried food consumption less than once, one to three times, and four or more times a week (P<0.001 for interaction); and the odds ratios (95% confidence intervals) for obesity per 10 risk alleles were 1.61 (1.40 to 1.87), 2.12 (1.73 to 2.59), and 2.72 (2.12 to 3.48) across the three categories of consumption (P=0.002 for interaction). In addition, the variants in or near genes highly expressed or known to act in the central nervous system showed significant interactions with fried food consumption, with the FTO (fat mass and obesity associated) variant showing the strongest result (P<0.001 for interaction). Conclusion: Our findings suggest that consumption of fried food could interact with genetic background in relation to obesity, highlighting the particular importance of reducing fried food consumption in individuals genetically predisposed to obesity
Asymptotic Behavior for a Nematic Liquid Crystal Model with Different Kinematic Transport Properties
We study the asymptotic behavior of global solutions to hydrodynamical
systems modeling the nematic liquid crystal flows under kinematic transports
for molecules of different shapes. The coupling system consists of
Navier-Stokes equations and kinematic transport equations for the molecular
orientations. We prove the convergence of global strong solutions to single
steady states as time tends to infinity as well as estimates on the convergence
rate both in 2D for arbitrary regular initial data and in 3D for certain
particular cases
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