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

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 Grüneisen 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

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 $0.6627\pm0.0002$, where the exact value is $h_2=0.662798972834$. For three-dimensional lattice with periodic condition, our numerical result is $0.7847\pm0.0014$, {which agrees with the best known bound $0.7653 \leq h_3 \leq 0.7862$.}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 $T^d$ by $S^d$ and $T^{d_k}\times S^{d_x}$ by $S^{d_k+d_x}$ 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, 6536–6537], 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 platinum–DNA 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_(1−x)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.Rôle de la vasopressine dans l'altération de l'excrétion de l'eau par le rat conscient atteint de cirrhose expérimentale. Cette étude a été entreprise pour élucider le mécanisme de l'altération de l'excrétion de l'eau au cours de la cirrhose du rat. Des rats conscients chez lesquels une cirrhose prouvée histologiquement a été induite par le tétrachlorure et le phénobarbital ont été comparés à des rats contrôles recevant seulement le phénobarbital. L'altération de l'excrétion de l'eau dans la cirrhose expérimentale a été vérifiée par l'hyponatrémie basale (138 vs. 147 mEq/litre, P < 0,005) et le défaut d'excrétion d'une charge en eau (osmolalité urinaire minimale 262 vs. 100 mOsm/kg; 58 vs. 102% de la charge d'eau sont excrétés, P < 0,001). Pour élucider le mécanisme de cette altération de l'excrétion de l'eau le débit de filtration glomérulaire (GFR), le débit sanguin rénal (RBF) et les concentrations de vasopressine (VP) ont été mesurés. Dans la cirrhose GFR est normal alors que RBF est diminué (4,5 vs. 6,8 ml/min/gm, P < 0,01). VP est plus élevée chez les rats cirrhotiques (1,61 vs. 0,71 pg/ml, P < 0,025). La signification des modifications de l'hémodynamique rénale et de l'augmentation de VP a été évaluée en créant des cirrhoses chez des rats sans VP de la souche Brattleboro (DI). Malgré des modifications histologiques, biochimiques et hémodynamiques rénales qui sont comparables à celles des rats dont la neurohypophyse est intacte, les rats DI cirrhotiques n'ont pas d'altération de l'excrétion de l'eau. Pour connaître la cause de l'augmentation de VP dans la cirrhose expérimentale le volume sanguin et l'hémodynamique systémique ont été étudiés. Quoique le volume plasmatique soit augmenté dans la cirrhose expérimentale (4,3 vs. 3,0 ml/100 g, P < 0,05) les rats cirrhotiques ont des résistances périphériques inférieures (0,37 vs. 0,42mm Hg/ml/min/kg, P < 0,05) et une pression artérielle moyenne inférieure (104 vs. 120mm Hg, P < 0,001) à celles des rats contrôles. Ces résultats indiquent que la cirrhose expérimentale du rat comporte une altération de l'excrétion de l'eau associée à une hémodynamique rénale anormale et à des concentrations de VP augmentées. L'altération de l'excrétion de l'eau, cependant, a la vasopressione comme seul médiateur. Le stimulus non osmolaire de la libération de VP pourrait être l'anomalie de l'hémodynamique systémique

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