406 research outputs found
Exact solution of a model DNA-inversion genetic switch with orientational control
DNA inversion is an important mechanism by which bacteria and bacteriophage
switch reversibly between phenotypic states. In such switches, the orientation
of a short DNA element is flipped by a site-specific recombinase enzyme. We
propose a simple model for a DNA inversion switch in which recombinase
production is dependent on the switch state (orientational control). Our model
is inspired by the fim switch in Escherichia coli. We present an exact
analytical solution of the chemical master equation for the model switch, as
well as stochastic simulations. Orientational control causes the switch to
deviate from Poissonian behaviour: the distribution of times in the on state
shows a peak and successive flip times are correlated.Comment: Revised version, accepted for publicatio
Fluctuations of internal energy flow in a vibrated granular gas
The non-equilibrium fluctuations of power flux in a fluidized granular media
have been recently measured in an experiment [Phys. Rev. Lett. 92, 164301,
2004], which was announced to be a verification of the Fluctuation Relation
(FR) by Gallavotti and Cohen. An effective temperature was also identified and
proposed to be a useful probe for such non equilibrium systems. We explain
these results in terms of a two temperature Poisson process. Within this model,
supported by independent Molecular Dynamics simulations, power flux
fluctuations do not satisfy the FR and the nature of the effective temperature
is clarified. In the pursue of a hypothetical global quantity fulfilling the
FR, this points to the need of considering other candidates than the power
flux.Comment: accepted for publication on Physical Review Lette
Active mechanics reveal molecular-scale force kinetics in living oocytes
Active diffusion of intracellular components is emerging as an important
process in cell biology. This process is mediated by complex assemblies of
molecular motors and cytoskeletal filaments that drive force generation in the
cytoplasm and facilitate enhanced motion. The kinetics of molecular motors have
been precisely characterized in-vitro by single molecule approaches, however,
their in-vivo behavior remains elusive. Here, we study the active diffusion of
vesicles in mouse oocytes, where this process plays a key role in nuclear
positioning during development, and combine an experimental and theoretical
framework to extract molecular-scale force kinetics (force, power-stroke, and
velocity) of the in-vivo active process. Assuming a single dominant process, we
find that the nonequilibrium activity induces rapid kicks of duration 300 s resulting in an average force of 0.4 pN on vesicles
in in-vivo oocytes, remarkably similar to the kinetics of in-vitro myosin-V.
Our results reveal that measuring in-vivo active fluctuations allows extraction
of the molecular-scale activity in agreement with single-molecule studies and
demonstrates a mesoscopic framework to access force kinetics.Comment: 20 pages, 4 figures, see ancillary files for Supplementary Materials,
* equally contributing author
IMMEDIATE FIXED REHABILITATION OF SEVERE MAXILLARY ATROPHY USING TILTED TRANS-SINUS IMPLANTS WITH OR WITHOUT SINUS BONE GRAFTING: FOUR-YEAR RESULTS FROM A RANDOMIZED CONTROLLED TRIAL
Fluctuations in granular gases
A driven granular material, e.g. a vibrated box full of sand, is a stationary
system which may be very far from equilibrium. The standard equilibrium
statistical mechanics is therefore inadequate to describe fluctuations in such
a system. Here we present numerical and analytical results concerning energy
and injected power fluctuations. In the first part we explain how the study of
the probability density function (pdf) of the fluctuations of total energy is
related to the characterization of velocity correlations. Two different regimes
are addressed: the gas driven at the boundaries and the homogeneously driven
gas. In a granular gas, due to non-Gaussianity of the velocity pdf or lack of
homogeneity in hydrodynamics profiles, even in the absence of velocity
correlations, the fluctuations of total energy are non-trivial and may lead to
erroneous conclusions about the role of correlations. In the second part of the
chapter we take into consideration the fluctuations of injected power in driven
granular gas models. Recently, real and numerical experiments have been
interpreted as evidence that the fluctuations of power injection seem to
satisfy the Gallavotti-Cohen Fluctuation Relation. We will discuss an
alternative interpretation of such results which invalidates the
Gallavotti-Cohen symmetry. Moreover, starting from the Liouville equation and
using techniques from large deviation theory, the general validity of a
Fluctuation Relation for power injection in driven granular gases is
questioned. Finally a functional is defined using the Lebowitz-Spohn approach
for Markov processes applied to the linear inelastic Boltzmann equation
relevant to describe the motion of a tracer particle. Such a functional results
to be different from injected power and to satisfy a Fluctuation Relation.Comment: 40 pages, 18 figure
Is it possible to experimentally verify the fluctuation relation? A review of theoretical motivations and numerical evidence
The theoretical motivations to perform experimental tests of the stationary
state fluctuation relation are reviewed. The difficulties involved in such
tests, evidenced by numerical simulations, are also discussed.Comment: 36 pages, 4 figures. Extended version of a presentation to the
discussion "Is it possible to experimentally verify the fluctuation
theorem?", IHP, Paris, December 1, 2006. Comments are very welcom
Money, Finance and Demography: The Consequences of Ageing
A significant ageing trend can be observed in Europe and in other parts of the world. Fertility is decreasing and life expectancy increasing. The impact of migration is growing. The book deals with the implications for financial markets of these demographic trends. Leading economists and financial experts from Europe and the United States evaluate the challenges to public pension systems and the private pension industry. Based on long-term projections of productivity and employment they look at potential growth in GDP per capita and implications for savings and wealth. Pension fund portfolio management is discussed together with the ability of capital markets to serve retirement-financing purposes. Fiscal as well as financial sustainability are analysed in depth. The roles of global imbalances and international capital movements are included. Most chapters also discuss policy implications - in particular with regard to how pension saving incentives and rules and incentives for retirement should be in order to ensure fiscal and financial sustainability. All contributions in the book are based on presentations at the 26th SUERF Colloquium on "Money, Finance and Demography - the Consequences of Ageing" held on 12-14 October, 2006 in Lisbon sponsored by Banco de Portugal and Millennium bcp and in cooperation with the Universidade Nova de Lisboa.
Autoimmune cytopenias in chronic lymphocytic leukemia
Chronic lymphocytic leukemia (CLL) is frequently complicated by secondary autoimmune cytopenias (AIC) represented by autoimmune hemolytic anemia (AIHA), immune thrombocytopenia (ITP), pure red cell aplasia and autoimmune granulocytopenia. The distinction of immune cytopenias from cytopenias due to bone marrow infiltration, usually associated with a worse outcome and often requiring a different treatment, is mandatory. AIHA and ITP are more frequently found in patients with unfavorable biological risk factors for CLL. AIC secondary to CLL respond less favorably to standard treatments than their primary forms, and treating the underlying CLL with chemotherapy or monoclonal antibodies may ultimately be necessary
Does urethral competence affect urodynamic voiding parameters in women with prolapse?
Aims To (1) compare voiding parameters and (2) correlate symptoms and urodynamic findings in women with pelvic organ prolapse (POP) and varying degrees of urethral competence. Methods We compared three groups of women with stages II–IV POP. Groups 1 and 2 were symptomatically stress continent women participating in the Colpopexy and Urinary Reduction Efforts (CARE) trial; during prolapse reduction before sacrocolpopexy, Group 1 (n = 67) did not have and Group 2 (n = 84) had urodynamic stress incontinence (USI) during prolapse reduction. Group 3 participants (n = 74), recruited specifically for this study, had stress urinary incontinence (SUI) symptoms and planned sacrocolpopexy. Participants completed standardized uroflowmetry, pressure voiding studies, and validated symptom questionnaires. Results Subjects' median age was 61 years, median parity 3 and 87% had stage III or IV POP. Fourteen percent of women in Group 3 demonstrated USI without, and 70% with, prolapse reduction. Women in Groups 2 and 3 had more detrusor overactivity (DO) than Group 1 (17 and 24% vs. 6%, P = 0.02) and detrusor overactivity incontinence (DOI) (15 and 8% vs. 0%, P = 0.004). Based on the Blaivis–Groutz nomogram, 60% of all women were obstructed. Post-void residual volume (PVR), peak flow rate, detrusor pressure at peak flow, voiding mechanisms, voiding patterns, obstruction and urinary retention did not differ among groups. Women in Group 3 had higher irritative and obstructive symptom scores than Group 1 or 2; neither score differed by presence of DO nor obstruction, respectively. Conclusion Women with POP have significant rates of urodynamic obstruction and retention, independent of their continence status. Symptoms of obstruction and retention correlate poorly with urodynamic findings. Neurourol. Urodynam. 26:1030–1035, 2007. © 2007 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57365/1/20436_ftp.pd
Import of cytochrome c into mitochondria
The import of cytochrome c into mitochondria can be resolved into a number of discrete steps. Here we report on the covalent attachment of heme to apocytochrome c by the enzyme cytochrome c heme lyase in mitochondria from Neurospora crassa.
A new method was developed to measure directly the linkage of heme to apocytochrome c. This method is independent of conformational changes in the protein accompanying heme attachment. Tryptic peptides of [35S]cysteine-labelled apocytochrome c, and of enzymatically formed holocytochrome c, were resolved by reverse-phase HPLC. The cysteine-containing peptide to which heme was attached eluted later than the corresponding peptide from apocytochrome c and could be quantified by counting 35S radioactivity as a measure of holocytochrome c formation. Using this procedure, the covalent attachment of heme to apocytochrome c, which is dependent on the enzyme cytochrome c heme lyase, could be measured. Activity required heme (as hemin) and could be reversibly inhibited by the analogue deuterohemin. Holocytochrome c formation was stimulated 5–10-fold by NADH > NADPH > glutathione and was independent of a potential across the inner mitochondrial membrane. NADH was not required for the binding of apocytochrome c to mitochondria and was not involved in the reduction of the cysteine thiols prior to heme attachment. Holocytochrome c formation was also dependent on a cytosolic factor that was necessary for the heme attaching step of cytochrome c import. The factor was a heat-stable, protease-insensitive, low-molecular-mass component of unknown function.
Cytochrome c heme lyase appeared to be a soluble protein located in the mitochondrial intermembrane space and was distinct from the previously identified apocytochrome c binding protein having a similar location. A model is presented in which the covalent attachment of heme by cytochrome c heme lyase also plays an essential role in the import pathway of cytochrome c
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