1,849 research outputs found
Novel method for the analysis of clathrates
Recently various of applications of clathrates, such as the concentration of juices, water desalination and wastewater treatment have gained the attention in industry and research alike. In this paper we present a novel method based on photoacoustic spectroscopy for the analysis of clathrates in aqueous environments. The herein proposed self-referencing method poses a simple and robust approach identifying and determining the formation of clathrates via the measurement of the GrĂŒneisen coefficient using a PVDF-based photoacoustic spectroscope. This research holds high potential for industrial applications of clathrates helping to save time, energy and resources during the clathrate forming process by indicating clathrate formation
Shear-induced reaction-limited aggregation kinetics of Brownian particles at arbitrary concentrations
The aggregation of interacting Brownian particles in sheared concentrated
suspensions is an important issue in colloid and soft matter science per se.
Also, it serves as a model to understand biochemical reactions occurring in
vivo where both crowding and shear play an important role. We present an
effective medium approach within the Smoluchowski equation with shear which
allows one to calculate the encounter kinetics through a potential barrier
under shear at arbitrary colloid concentrations. Experiments on a model
colloidal system in simple shear flow support the validity of the model in the
range considered. By generalizing Kramers' rate theory to the presence of
collective hydrodynamics, our model explains the significant increase in the
shear-induced reaction-limited aggregation kinetics upon increasing the colloid
concentration
Approximating the monomer-dimer constants through matrix permanent
The monomer-dimer model is fundamental in statistical mechanics. However, it
is #P-complete in computation, even for two dimensional problems. A
formulation in matrix permanent for the partition function of the monomer-dimer
model is proposed in this paper, by transforming the number of all matchings of
a bipartite graph into the number of perfect matchings of an extended bipartite
graph, which can be given by a matrix permanent. Sequential importance sampling
algorithm is applied to compute the permanents. For two-dimensional lattice
with periodic condition, we obtain , where the exact value is
. For three-dimensional lattice with periodic condition,
our numerical result is , {which agrees with the best known
bound .}Comment: 6 pages, 2 figure
Homotopy Theory of Strong and Weak Topological Insulators
We use homotopy theory to extend the notion of strong and weak topological
insulators to the non-stable regime (low numbers of occupied/empty energy
bands). We show that for strong topological insulators in d spatial dimensions
to be "truly d-dimensional", i.e. not realizable by stacking lower-dimensional
insulators, a more restrictive definition of "strong" is required. However,
this does not exclude weak topological insulators from being "truly
d-dimensional", which we demonstrate by an example. Additionally, we prove some
useful technical results, including the homotopy theoretic derivation of the
factorization of invariants over the torus into invariants over spheres in the
stable regime, as well as the rigorous justification of replacing by
and by as is common in the current
literature.Comment: 11 pages, 3 figure
Poly(ADP-ribose) polymerase-1 activity facilitates the dissociation of nuclear proteins from platinum-modified DNA
The affinity of the poly(ADP-ribose) polymerase-1 (PARP-1) for platinum-damaged DNA was first discovered during photo-cross-linking experiments using the photoactive compound Pt-BP6 [J. Am. Chem. Soc. 2004, 126, 6536â6537], an analogue of the anticancer drug cis-diamminedichloroplatinum(II), cisplatin. Although PARP inhibitors sensitize cancer cells to cisplatin, there are conflicting reports in the literature about their efficacy. In order to improve our understanding of the mechanism by which PARP inhibition might potentiate the cell-killing ability of cisplatin, and to shed light on the source of the discrepancy among different laboratories, we have in the present study probed the influence of three PARP inhibitors in four types of cancer cells, cervical (HeLa), testicular (NTera2), pancreatic (BxPC3), and osteosarcoma (U2OS), on the results of Pt-BP6 photo-cross-linking experiments and cytotoxicity assays. We find that the activity of PARP proteins following exposure to platinum-modified DNA results in the dissociation of DNA-bound proteins. PARP inhibitors were able to sensitize some, but not all, of the cell lines to cisplatin. This cell line-dependence and the potential consequences of PARP-initiated protein removal from platinumâDNA lesions are discussed. Control experiments revealed that NTera2 cells are especially sensitive to PARP inhibition
Ferromagnetism, glassiness, and metastability in a dilute dipolar-coupled magnet
We have measured the ac magnetic susceptibility of the model dilute dipolar-coupled Ising system LiHo_xY_(1âx)F_4. The x=0.46 material displays an ordinary ferromagnetic transition, while the x=0.045 and 0.167 samples are two very different magnetic glasses. Thermal relaxation times are more than five times longer for x=0.167 than for x=0.045. In addition, the more concentrated glass shows history dependence and metastability upon field cooling
ABCD transfer matrix model of Gaussian beam propagation in plano-concave optical microresonators
Plano-concave optical microresonators (PCMRs) are optical microcavities formed of one planar and one concave mirror separated by a spacer. PCMRs illuminated by Gaussian laser beams are used as sensors and filters in fields including quantum electrodynamics, temperature sensing, and photoacoustic imaging. To predict characteristics such as the sensitivity of PCMRs, a model of Gaussian beam propagation through PCMRs based on the ABCD matrix method was developed. To validate the model, interferometer transfer functions (ITFs) calculated for a range of PCMRs and beams were compared to experimental measurements. A good agreement was observed, suggesting the model is valid. It could therefore constitute a useful tool for designing and evaluating PCMR systems in various fields. The computer code implementing the model has been made available online
An investigation of standard thermodynamic quantities as determined via models of nuclear multifragmentation
Both simple and sophisticated models are frequently used in an attempt to
understand how real nuclei breakup when subjected to large excitation energies,
a process known as nuclear multifragmentation. Many of these models assume
equilibriumthermodynamics and produce results often interpreted as evidence of
a phase transition. This work examines one class of models and employs standard
thermodynamical procedure to explore the possible existence and nature of a
phase transition. The role of various terms, e.g. Coulomb and surface energy,
is discussed.Comment: 19 two-column format pages with 24 figure
Role of vasopressin in impaired water excretion in conscious rats with experimental cirrhosis
Role of vasopressin in impaired water excretion in conscious rats with experimental cirrhosis. The present study was undertaken to study the mechanism of impaired water excretion in experimental cirrhosis in the rat. Conscious rats in whom histologically proven cirrhosis was induced with carbon tetrachloride and phenobarbital were compared with control rats given phenobarbital alone. Impaired water excretion in experimental cirrhosis was verified by a basal hyponatremia (138 vs. 147 mEq/liter, P < 0.005) and an impaired excretion of water load (minimal urinary osmolality, 262 vs. 100 mOsm/kg; 58 vs. 102% of water load excreted, P < 0.001). To clarify the mechanism of this impaired water excretion, we measured glomerular filtration rate (GFR), renal blood flow (RBF), and vasopressin (VP) levels. In cirrhosis, GFR was normal but RBF was decreased (4.5 vs 6.8 ml/min/g, P < 0.01). VP levels were found to be higher in cirrhotic rats (1.61 vs. 0.71 pg/ml, P < 0.025). The significance of the impaired renal hemodynamics and the increase in VP was assessed by inducing cirrhosis in VP-free Brattle-boro (diabetes insipidus; DI) rats. Despite histologic, biochemical, and renal hemodynamic changes that were comparable to cirrhotic rats with an intact neurohypophysis, cirrhotic DI rats had no impairment in water excretion. To determine the cause of increased VP in experimental cirrhosis, we determined blood volume and systemic hemodynamics. Although plasma volume was greater in experimental cirrhosis (4.3 vs. 3.0 ml/100 g, P < 0.05), cirrhotic rats had a significantly lower peripheral resistance (0.37 vs. 0.42mm Hg/ml/min/kg, P < 0.05) and mean arterial pressure (104 vs. 120mm Hg, P < 0.001) than did control rats. These results document that experimental cirrhosis in the rat is associated with impaired renal water excretion in association with both abnormal renal hemodynamics and increased VP levels. The impaired water excretion, however, is solely VP mediated. The nonosmolar stimulus for VP release may be due to abnormal systemic hemodynamics.RĂŽle de la vasopressine dans l'altĂ©ration de l'excrĂ©tion de l'eau par le rat conscient atteint de cirrhose expĂ©rimentale. Cette Ă©tude a Ă©tĂ© entreprise pour Ă©lucider le mĂ©canisme de l'altĂ©ration de l'excrĂ©tion de l'eau au cours de la cirrhose du rat. Des rats conscients chez lesquels une cirrhose prouvĂ©e histologiquement a Ă©tĂ© induite par le tĂ©trachlorure et le phĂ©nobarbital ont Ă©tĂ© comparĂ©s Ă des rats contrĂŽles recevant seulement le phĂ©nobarbital. L'altĂ©ration de l'excrĂ©tion de l'eau dans la cirrhose expĂ©rimentale a Ă©tĂ© vĂ©rifiĂ©e par l'hyponatrĂ©mie basale (138 vs. 147 mEq/litre, P < 0,005) et le dĂ©faut d'excrĂ©tion d'une charge en eau (osmolalitĂ© urinaire minimale 262 vs. 100 mOsm/kg; 58 vs. 102% de la charge d'eau sont excrĂ©tĂ©s, P < 0,001). Pour Ă©lucider le mĂ©canisme de cette altĂ©ration de l'excrĂ©tion de l'eau le dĂ©bit de filtration glomĂ©rulaire (GFR), le dĂ©bit sanguin rĂ©nal (RBF) et les concentrations de vasopressine (VP) ont Ă©tĂ© mesurĂ©s. Dans la cirrhose GFR est normal alors que RBF est diminuĂ© (4,5 vs. 6,8 ml/min/gm, P < 0,01). VP est plus Ă©levĂ©e chez les rats cirrhotiques (1,61 vs. 0,71 pg/ml, P < 0,025). La signification des modifications de l'hĂ©modynamique rĂ©nale et de l'augmentation de VP a Ă©tĂ© Ă©valuĂ©e en crĂ©ant des cirrhoses chez des rats sans VP de la souche Brattleboro (DI). MalgrĂ© des modifications histologiques, biochimiques et hĂ©modynamiques rĂ©nales qui sont comparables Ă celles des rats dont la neurohypophyse est intacte, les rats DI cirrhotiques n'ont pas d'altĂ©ration de l'excrĂ©tion de l'eau. Pour connaĂźtre la cause de l'augmentation de VP dans la cirrhose expĂ©rimentale le volume sanguin et l'hĂ©modynamique systĂ©mique ont Ă©tĂ© Ă©tudiĂ©s. Quoique le volume plasmatique soit augmentĂ© dans la cirrhose expĂ©rimentale (4,3 vs. 3,0 ml/100 g, P < 0,05) les rats cirrhotiques ont des rĂ©sistances pĂ©riphĂ©riques infĂ©rieures (0,37 vs. 0,42mm Hg/ml/min/kg, P < 0,05) et une pression artĂ©rielle moyenne infĂ©rieure (104 vs. 120mm Hg, P < 0,001) Ă celles des rats contrĂŽles. Ces rĂ©sultats indiquent que la cirrhose expĂ©rimentale du rat comporte une altĂ©ration de l'excrĂ©tion de l'eau associĂ©e Ă une hĂ©modynamique rĂ©nale anormale et Ă des concentrations de VP augmentĂ©es. L'altĂ©ration de l'excrĂ©tion de l'eau, cependant, a la vasopressione comme seul mĂ©diateur. Le stimulus non osmolaire de la libĂ©ration de VP pourrait ĂȘtre l'anomalie de l'hĂ©modynamique systĂ©mique
The liquid to vapor phase transition in excited nuclei
For many years it has been speculated that excited nuclei would undergo a
liquid to vapor phase transition. For even longer, it has been known that
clusterization in a vapor carries direct information on the liquid- vapor
equilibrium according to Fisher's droplet model. Now the thermal component of
the 8 GeV/c pion + 197Au multifragmentation data of the ISiS Collaboration is
shown to follow the scaling predicted by Fisher's model, thus providing the
strongest evidence yet of the liquid to vapor phase transition.Comment: four pages, four figures, first two in color (corrected typo in Ref.
[26], corrected error in Fig. 4
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