Spatial Pattern Formation During Aggregation of the Slime Mould Dictyostelium discoideum

Stream formation and spiral wave behaviour during the aggregation of Dictyostelium discoideum (Dd) are studied in a model based on the Martiel-Goldbeter equations for cAMP relay, combined with chemotactic motion of Dd cells. The results show that stream formation occurs if the turnover rate of intracellular cAMP is increased. This increase in the turnover rate of cAMP[in] leads to a dependence of the speed of the cAMP wave on the cell density. We propose that this dependence of wave speed on cell density is the underlying mechanism for stream formation. Besides stream formation, increasing the turnover rate of cAMP[in] also results in a spiral wave period that decreases during aggregation, a phenomenon that is commonly observed in situ. Furthermore, the dependence of wave speed on cell density is measured empirically[ The speed of the cAMP wave is found to decrease as the wave travels from high to low cell density. This indicates that in situ, wave speed does depend on cell density

Local-field correction to one- and two-atom van der Waals interactions

Based on macroscopic quantum electrodynamics in linearly and causally responding media, we study the local-field corrected van der Waals potentials and forces for unpolarized ground-state atoms placed within a magnetoelectric medium of arbitrary size and shape. We start from general expressions for the van der Waals potentials in terms of the (classical) Green tensor of the electromagnetic field and the atomic polarizability and incorporate the local-field correction by means of the real-cavity model. In this context, special emphasis is given to the decomposition of the Green tensor into a medium part multiplied by a global local-field correction factor and, in the single-atom case, a part that only depends on the cavity characteristics. The result is used to derive general formulas for the local-field corrected van der Waals potentials and forces. As an application, we calculate the van der Waals potential between two ground-state atoms placed within magnetoelectric bulk material.Comment: 9 pages, 2 figures, corrections according to erratu

Factors associated with positive urine cultures in cats with subcutaneous ureteral bypass system implantation

Objectives The aims of this study were to report the postoperative incidence of subcutaneous ureteral bypass (SUB)-associated bacteriuria and risk factors in a large population of UK cats, to identify the commonly implicated isolates in these cases and to report associations of positive postoperative urine cultures with device occlusion or a need for further surgery. Methods Electronic clinical records were reviewed to identify cats with ureteral obstruction that underwent unilateral or bilateral SUB implantation between September 2011 and September 2019. In total, 118 client-owned cats were included in the study population. Information recorded included signalment, history, surgical and biochemical factors, urinalysis and culture results. Multivariable logistic regression was performed to identify variables associated with a positive postoperative culture. Results In total, 10 cats (8.5%) had a positive postoperative culture within 1 month postsurgery and 28 cats (23.7%) within 1 year postsurgery. Cats with a positive preoperative culture were significantly more likely to have a positive culture within 6 months postoperatively (odds ratio [OR] 4.09, 95% confidence interval [CI] 1.18–14.18; P = 0.026). Of the 14 cats with a positive preoperative culture, six (42.9%) returned a positive culture within 1 year postoperatively, and in four cases (66.7%) the same isolate was identified. Cats with a higher end-anaesthetic rectal temperature were significantly less likely to return a positive culture within 3 months (OR 0.398, 95% CI 0.205–0.772; P = 0.006) postsurgery. Cats culturing positive for Escherichia coli at any time point (OR 4.542, 95% CI 1.485–13.89; P = 0.008) were significantly more likely to have their implant removed or replaced. Conclusions and relevance Perioperative hypothermia and preoperative positive culture were independent predictors of a postoperative positive culture and this should be taken into consideration when managing these cases. Positive postoperative culture rates were higher than have previously been reported

Nail lacquer films’ surface energies and in vitro water-resistance and adhesion do not predict their in vivo residence

The in vivo residence of nail lacquers (which are ideal topical drug carriers for the treatment of nail diseases) determines their frequency of application, and is thereby expected to influence patient adherence and success of treatment. Thus in vitro measurements to indicate lacquers’ in vivo residence are routinely conducted during formulation development. However the literature on in vitro-in vivo correlations is severely limited. Thus, the aim of the work discussed in this paper was to investigate correlations between in vivo residence and in vitro film resistance to water, in vitro film adhesion and surface energy of lacquer films. In vivo measurements were conducted on fingernails in six volunteers. Seven commercially available nail lacquers were tested in commonly-used measurements. Correlations between in vivo residence and in vitro water resistance and adhesion were found to be extremely poor. The surface energies of the lacquer films (which were between 33 and 39 mJ/m2) were also not predictive of in vivo residence. High density polyethylene (HDPE) sheet – whose surface energy was determined to be similar to that of the human nailplate – was found to be a suitable model for the nailplate (when investigating surface energy) and was used in a number of experiments

Models of Dictyostelium discoideum aggregation

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Templeting of Thin Films Induced by Dewetting on Patterned Surfaces

The instability, dynamics and morphological transitions of patterns in thin liquid films on periodic striped surfaces (consisting of alternating less and more wettable stripes) are investigated based on 3-D nonlinear simulations that account for the inter-site hydrodynamic and surface-energetic interactions. The film breakup is suppressed on some potentially destabilizing nonwettable sites when their spacing is below a characteristic lengthscale of the instability, the upper bound for which is close to the spinodal lengthscale. The thin film pattern replicates the substrate surface energy pattern closely only when, (a) the periodicity of substrate pattern matches closely with the characteristic lengthscale, and (b) the stripe-width is within a range bounded by a lower critical length, below which no heterogeneous rupture occurs, and an upper transition length above which complex morphological features bearing little resemblance to the substrate pattern are formed.Comment: 5 pages TeX (REVTeX 4), other comments: submitted to Phys. Rev.Let

Surface thermodynamic homeostasis of salivary conditioning films through polar–apolar layering

Salivary conditioning films (SCFs) form on all surfaces exposed to the oral cavity and control diverse oral surface phenomena. Oral chemotherapeutics and dietary components present perturbations to SCFs. Here we determine the surface energetics of SCFs through contact angle measurements with various liquids on SCFs following perturbations with a variety of chemotherapeutics as well as after renewed SCF formation. Sixteen-hour SCFs on polished enamel surfaces were treated with a variety of chemotherapeutics, including toothpastes and mouthrinses. After treatment with chemotherapeutics, a SCF was applied again for 3 h. Contact angles with four different liquids on untreated and treated SCF-coated enamel surfaces were measured and surface free energies were calculated. Perturbations either caused the SCF to become more polar or more apolar, but in all cases, renewed SCF formation compensated these changes. Thus, a polar SCF attracts different salivary proteins or adsorbs proteins in a different conformation to create a more apolar SCF surface after renewed SCF formation and vice versa for apolar SCFs. This polar–apolar layering in SCF formation presents a powerful mechanism in the oral cavity to maintain surface thermodynamic homeostasis—defining oral surface properties within a narrow, biological range and influencing chemotherapeutic strategies. Surface chemical changes brought about by dietary or chemotherapeutic perturbations to SCFs make it more polar or apolar, but new SCFs are rapidly formed compensating for changes in surface energetics

Streaming instability of slime mold amoebae: An analytical model

During the aggregation of amoebae of the cellular slime mould Dictyostelium, the interaction of chemical waves of the signaling molecule cAMP with cAMP-directed cell movement causes the breakup of a uniform cell layer into branching patterns of cell streams. Recent numerical and experimental investigations emphasize the pivotal role of the cell-density dependence of the chemical wave speed for the occurrence of the streaming instability. A simple, analytically tractable, model of Dictyostelium aggregation is developed to test this idea. The interaction of cAMP waves with cAMP-directed cell movement is studied in the form of coupled dynamics of wave front geometries and cell density. Comparing the resulting explicit instability criterion and dispersion relation for cell streaming with the previous findings of model simulations and numerical stability analyses, a unifying interpretation of the streaming instability as a cAMP wave-driven chemotactic instability is proposed

Is Perioperative Hypothermia a Risk Factor for Post-Cesarean Infection?

Objective: To determine whether hypothermia during Cesarean delivery is a risk factor for postoperative infection. Methods: An historical cohort investigation was conducted on all women delivered by Cesarean at our center during 2001. Initial recovery-room temperature, taken via the oral or axillary route, was used as a surrogate for intraoperative temperature. Adding 0.5(°)C to axillary temperatures generated oral temperature equivalents. Women with chorioamnionitis were excluded, as were those with an initial recovery-room temperature that exceeded 37.9(°)C or was recorded more than 20 minutes after the end of surgery. Prophylactic antibiotics (cefazolin, 1 g) were given during Cesarean delivery. Results: A total of 42 women (7.6%) were diagnosed with postoperative infections. Infections included endometritis (n= 25), wound abscess (n = 7), wound cellulitis (n = 7) and urinary tract infection (UTI) (n = 4). No cases of septic pelvic thrombophlebitis or pelvic abscess occurred. One woman had both endometritis and a UTI. Mean temperatures were higher, rather than lower, for women who subsequently had postoperative infections compared with those who did not (36.4 ± 0.8(°)Cvs. 35.9 ± 0.7(°)C; p < 0.001). Mean temperatures for the various postoperative infections were as follows: endometritis, 36.5 ± 0.8(°)C (p < 0.001 vs. uninfected group); wound abscess 36.0 ± 0.8(°)C (p = 0.63); wound cellulitis, 36.3 ± 0.6(°)C (p = 0.14); UTI, 36.7 ± 0.9(°)C (p = 0.04). Conclusions: Women who develop post-Cesarean infections have higher initial recovery-room temperatures than those who do not develop such infections. This suggests the presence of subclinical infection at the time of Cesarean. Evaluating whether intraoperative warming has any role during Cesarean delivery requires a randomized clinical trial