Viscoelastic flow asymmetries in a helical static mixer and their impact on mixing performance

Helical static mixers are often used during the processing of formulated products with complex rheological properties, such as viscoelasticity. Previous experimental studies have highlighted that increasing the viscoelasticity of the flow hinders the mixing performance in the laminar flow regime. In this study, we use computational fluid dynamics to investigate the flow of a FENE-CR model fluid in a helical static mixer. The numerical results show clearly that the reduced mixing performance is caused by flow distribution asymmetries which develop at the mixer element intersections. The results allow us to quantify the degree of asymmetry for the range of conditions studied, which is correlated with the quantified mixing performance for each simulation. The mixing is quantified using a Lagrangian particle tracking technique, and a new mixing index is defined based on the mean nearest distance between the two sets of tracked particles. The results show that the asymmetry parameter does not follow a pitchfork bifurcation, as it typically does for elastic instabilities in symmetrical geometries such as the cross-slot. For low values of the extensibility parameter, L2, the flow remained (Eulerian) steady for all Reynolds Re and Weissenberg Wi numbers studied. At fixed Re and Wi, increasing L2 causes the flow to become transient and greatly increases the magnitude of the asymmetry. The results presented in this study help us to understand the effects that viscoelasticity can cause in mixing processes

Acoustic black holes for relativistic fluids

We derive a new acoustic black hole metric from the Abelian Higgs model. In the non-relativistic limit, while the Abelian Higgs model becomes the Ginzburg-Landau model, the metric reduces to an ordinary Unruh type. We investigate the possibility of using (type I and II) superconductors as the acoustic black holes. We propose to realize experimental acoustic black holes by using spiral vortices solutions from the Navier-stokes equation in the non-relativistic classical fluids.Comment: 16 pages. typos corrected, contents expande

Analytical study on holographic superconductors in external magnetic field

We investigate the holographic superconductors immersed in an external magnetic field by using the analytical approach. We obtain the spatially dependent condensate solutions in the presence of the magnetism and find analytically that the upper critical magnetic field satisfies the relation given in the Ginzburg-Landau theory. We observe analytically the reminiscent of the Meissner effect where the magnetic field expels the condensate. Extending to the D-dimensional Gauss-Bonnet AdS black holes, we examine the influence given by the Gauss-Bonnet coupling on the condensation. Different from the positive coupling, we find that the negative Gauss-Bonnet coupling enhances the condensation when the external magnetism is not strong enough.Comment: revised version, to appear in JHE

Fracturing ranked surfaces

Discretized landscapes can be mapped onto ranked surfaces, where every element (site or bond) has a unique rank associated with its corresponding relative height. By sequentially allocating these elements according to their ranks and systematically preventing the occupation of bridges, namely elements that, if occupied, would provide global connectivity, we disclose that bridges hide a new tricritical point at an occupation fraction $p=p_{c}$, where $p_{c}$ is the percolation threshold of random percolation. For any value of $p$ in the interval $p_{c}< p \leq 1$, our results show that the set of bridges has a fractal dimension $d_{BB} \approx 1.22$ in two dimensions. In the limit $p \rightarrow 1$, a self-similar fracture is revealed as a singly connected line that divides the system in two domains. We then unveil how several seemingly unrelated physical models tumble into the same universality class and also present results for higher dimensions

Isotope effect on the transition temperature TcT_c in Fe-based superconductors: the current status

The results of the Fe isotope effect (Fe-IE) on the transition temperature $T_c$ obtained up to date in various Fe-based high temperature superconductors are summarized and reanalyzed by following the approach developed in [Phys. Rev. B 82, 212505 (2010)]. It is demonstrated that the very controversial results for Fe-IE on $T_c$ are caused by small structural changes occurring simultaneously with the Fe isotope exchange. The Fe-IE exponent on $T_c$ [$\alpha_{\rm Fe}=-(\Delta T_c/T_c)/(\Delta M/M)$, $M$ is the isotope mass] needs to be decomposed into two components with the one related to the structural changes ($\alpha_{\rm Fe}^{\rm str}$) and the genuine (intrinsic) one ($\alpha_{\rm Fe}^{\rm int}$). The validity of such decomposition is further confirmed by the fact that $\alpha_{\rm Fe}^{\rm int}$ coincides with the Fe-IE exponent on the characteristic phonon frequencies $\alpha_{\rm Fe}^{\rm ph}$ as is reported in recent EXAFS and Raman experiments.Comment: 7 pages, 4 figures. The paper is partially based on the results published in [New J. Phys. 12, 073024 (2010) = arXiv:1002.2510] and [Phys. Rev. B 82, 212505 (2010) = arXiv:1008.4540

Driven coherent oscillations of a single electron spin in a quantum dot

The ability to control the quantum state of a single electron spin in a quantum dot is at the heart of recent developments towards a scalable spin-based quantum computer. In combination with the recently demonstrated exchange gate between two neighbouring spins, driven coherent single spin rotations would permit universal quantum operations. Here, we report the experimental realization of single electron spin rotations in a double quantum dot. First, we apply a continuous-wave oscillating magnetic field, generated on-chip, and observe electron spin resonance in spin-dependent transport measurements through the two dots. Next, we coherently control the quantum state of the electron spin by applying short bursts of the oscillating magnetic field and observe about eight oscillations of the spin state (so-called Rabi oscillations) during a microsecond burst. These results demonstrate the feasibility of operating single-electron spins in a quantum dot as quantum bits.Comment: Total 25 pages. 11 pages main text, 5 figures, 9 pages supplementary materia

Abdominal Wound Dehiscence in Adults: Development and Validation of a Risk Model

Background: Several studies have been performed to identify risk factors for abdominal wound dehiscence. No risk model had yet been developed for the general surgical population. The objective of the present study was to identify independent risk factors for abdominal wound dehiscence and to develop a risk model to recognize high-risk patients. Identification of high-risk patients offers opportunities for intervention strategies. Methods: Medical registers from January 1985 to December 2005 were searched. Patients who had primarily undergone appendectomies or nonsurgical (e.g., urological) operations were excluded. Each patient with abdominal wound dehiscence was matched with three controls by systematic random sampling. Putative relevant patient-related, operation-related, and postoperative variables were evaluated in univariate analysis and subsequently entered in multivariate stepwise logistic regression models to delineate major independent predictors of abdominal wound dehiscence. A risk model was developed, which was validated in a population of patients who had undergone operation between January and December 2006. Results: A total of 363 cases and 1,089 controls were analyzed. Major independent risk factors were age, gender, chronic pulmonary disease, ascites, jaundice, anemia, emergency surgery, type of surgery, postoperative coughing, and wound infection. In the validation population, risk scores were significantly higher (P < 0.001) for patients with abdominal wound dehiscence (n = 19) compared to those without (n = 677). Resulting scores ranged from 0 to 8.5, and the risk for abdominal wound dehiscence over this range increased exponentially from 0.02% to 70.1%. Conclusions: The validated risk model shows high predictive value for abdominal wound dehiscence and may help to identify patients at increased risk

Association of Gender with Clinical Expression, Quality of Life, Disability, and Depression and Anxiety in Patients with Systemic Sclerosis

OBJECTIVES: To assess the association of gender with clinical expression, health-related quality of life (HRQoL), disability, and self-reported symptoms of depression and anxiety in patients with systemic sclerosis (SSc). METHODS: SSc patients fulfilling the American College of Rheumatology and/or the Leroy and Medsger criteria were assessed for clinical symptoms, disability, HRQoL, self-reported symptoms of depression and anxiety by specific measurement scales. RESULTS: Overall, 381 SSc patients (62 males) were included. Mean age and disease duration at the time of evaluation were 55.9 (13.3) and 9.5 (7.8) years, respectively. One-hundred-and-forty-nine (40.4%) patients had diffuse cutaneous SSc (dcSSc). On bivariate analysis, differences were observed between males and females for clinical symptoms and self-reported symptoms of depression and anxiety, however without reaching statistical significance. Indeed, a trend was found for higher body mass index (BMI) (25.0 [4.1] vs 23.0 [4.5], p = 0.013), more frequent dcSSc, echocardiography systolic pulmonary artery pressure >35 mmHg and interstitial lung disease in males than females (54.8% vs 37.2%, p = 0.010; 24.2% vs 10.5%, p = 0.003; and 54.8% vs 41.2%, p = 0.048, respectively), whereas calcinosis and self-reported anxiety symptoms tended to be more frequent in females than males (36.0% vs 21.4%, p = 0.036, and 62.3% vs 43.5%, p = 0.006, respectively). On multivariate analysis, BMI, echocardiography PAP>35 mmHg, and anxiety were the variables most closely associated with gender. CONCLUSIONS: In SSc patients, male gender tends to be associated with diffuse disease and female gender with calcinosis and self-reported symptoms of anxiety. Disease-associated disability and HRQoL were similar in both groups

A novel underuse model shows that inactivity but not ovariectomy determines the deteriorated material properties and geometry of cortical bone in the tibia of adult rats

Our goal in this study was to determine to what extent the physiologic consequences of ovariectomy (OVX) in bones are exacerbated by a lack of daily activity such as walking. We forced 14-week-old female rats to be inactive for 15 weeks with a unique experimental system that prevents standing and walking while allowing other movements. Tibiae, femora, and 4th lumbar vertebrae were analyzed by peripheral quantitative computed tomography (pQCT), microfocused X-ray computed tomography (micro-CT), histology, histomorphometry, Raman spectroscopy, and the three-point bending test. Contrary to our expectation, the exacerbation was very much limited to the cancellous bone parameters. Parameters of femur and tibia cortical bone were affected by the forced inactivity but not by OVX: (1) cross-sectional moment of inertia was significantly smaller in Sham-Inactive rat bones than that of their walking counterparts; (2) the number of sclerostin-positive osteocytes per unit cross-sectional area was larger in Sham-Inactive rat bones than in Sham-Walking rat bones; and (3) material properties such as ultimate stress of inactive rat tibia was lower than that of their walking counterparts. Of note, the additive effect of inactivity and OVX was seen only in a few parameters, such as the cancellous bone mineral density of the lumbar vertebrae and the structural parameters of cancellous bone in the lumbar vertebrae/tibiae. It is concluded that the lack of daily activity is detrimental to the strength and quality of cortical bone in the femur and tibia of rats, while lack of estrogen is not. Our inactive rat model, with the older rats, will aid the study of postmenopausal osteoporosis, the etiology of which may be both hormonal and mechanical