Using light to control the interactions between self-rotating assemblies of active gels

Polymer gels undergoing the oscillating Belousov-Zhabotinsky (BZ) reaction exhibit an autonomous, periodic swelling and deswelling, where the mechanical oscillations are driven by the chemical reaction within the polymer network. Using computer simulations, we show that these BZ gels can undergo a form of auto-chemotaxis, enabling the gels to spontaneously move in response to self-generated chemical gradients. Focusing on four millimeter-sized pieces of these BZ gels, we show that the pieces can organize into self-rotating clusters that resemble a moving pinwheel or gear. By analyzing the factors that promote the formation of a single self-rotating cluster, we attempt to design systems of multiple, interacting gears. We show that light, which suppresses the oscillations of the gels, can be harnessed to promote the formation of two self-rotating clusters. These studies point to a novel form of photo-chemo-mechanical transduction, where light is utilized to control the conversion of chemical and mechanical energy in the system. Moreover, the interaction between the BZ gel gears reveals a new form of entrainment between these moving units. Namely, their coordinated motion is achieved through chemical coupling or communication, rather than a mechanical coupling. These findings can lead to the formation of chemically “communicating” devices that can be programmed to perform autonomous work through the use of light.     

The investigation of the steady stage of steel fretting

The effects of slip length, frequency, surface pressure and shape of the longitudinal oscillatory motion on the fretting wear of steel were investigated by a specially designed fretting apparatus using an M.T.S. closed loop axial hydraulic testing system.

The rate of fretting wear in the steady stage was found to increase with increasing slip length and specific surface pressure and to decrease with increasing cyclic frequency and material hardness. The wave shape of the oscillatory motion does not appear to affect the wear rate.

Increased slip, greater surface pressure and lower cycling frequency all promote the adhesion mechanism of fretting. With higher frequencies decreased slip and low surface pressures, the product of fretting wear is mainly oxides and oxidation is the leading wear mechanism.     

Simultaneous segmentation of prostatic zones using Active Appearance Models with multiple coupled levelsets

In this work we present an improvement to the popular Active Appearance Model (AAM) algorithm, that we call the Multiple-Levelset AAM (MLA). The MLA can simultaneously segment multiple objects, and makes use of multiple levelsets, rather than anatomical landmarks, to define the shapes. AAMs traditionally define the shape of each object using a set of anatomical landmarks. However, landmarks can be difficult to identify, and AAMs traditionally only allow for segmentation of a single object of interest. The MLA, which is a landmark independent AAM, allows for levelsets of multiple objects to be determined and allows for them to be coupled with image intensities. This gives the MLA the flexibility to simulataneously segmentation multiple objects of interest in a new image.In this work we apply the MLA to segment the prostate capsule, the prostate peripheral zone (PZ), and the prostate central gland (CG), from a set of 40 endorectal, T2-weighted MRI images. The MLA system we employ in this work leverages a hierarchical segmentation framework, so constructed as to exploit domain specific attributes, by utilizing a given prostate segmentation to help drive the segmentations of the CG and PZ, which are embedded within the prostate. Our coupled MLA scheme yielded mean Dice accuracy values of .81, .79 and .68 for the prostate, CG, and PZ, respectively using a leave-one-out cross validation scheme over 40 patient studies. When only considering the midgland of the prostate, the mean DSC values were .89, .84, and .76 for the prostate, CG, and PZ respectively.     

Effect of initial powder type on the hydrogen storage properties of high-pressure torsion consolidated Mg

While severe plastic deformation (SPD) on bulk samples has been widely applied for modifying the H-sorption properties, there has been little attention towards the use of SPD on powder materials. In this context, the aim of the present work was to compare the H-storage properties of high-pressure torsion (HPT) consolidated products obtained from two distinct Mg powder precursors: atomized micro-sized and condensed ultrafine powder particles. The results showed that the nature of the initial powder precursor had a pronounced effect on the H-sorption behavior. The HPT product obtained from the condensed ultrafine powder showed faster absorption kinetics than the consolidated product obtained from the atomized powder. However, the HPT product obtained from atomized powder could absorb more hydrogen and showed faster desorption kinetics corresponding to a lower activation energy. These results are discussed by taking into account the effectiveness of the HPT process to refine the grain sizes and differences in the dispersion of fine MgO oxide particles.     

On the optimal design of water distribution networks: a practical MINLP approach

We propose a practical solution method for real-world instances of a water-network optimization problem with fixed topology using a nonconvex continuous NLP (NonLinear Programming) relaxation and a MINLP (Mixed Integer NonLinear Programming) search. Our approach employs a relatively simple and accurate model that pays some attention to the requirements of the solvers that we employ. Our view is that in doing so, with the goal of calculating only good feasible solutions, complicated algorithmics can be confined to the MINLP solver. We report successful computational experience using available open-source MINLP software on problems from the literature and on difficult real-world instances. An important contribution of this paper is that the solutions obtained, besides being low cost, are immediately usable in practice because they are characterized by an allocation of diameters to pipes that leads to a correct hydraulic operation of the network. This is not the case for most of the other methods presented in the literature.     

On Homogeneous Nucleation of Dislocation Loops in Nanocrystalline Materials

In this article, we readdress the question of homogeneous nucleation of dislocation loops in the context of nanocrystalline materials. In this case, the commonly adopted assumption of an infinite medium is no longer valid, and image forces on dislocations must be accounted for in the analysis. An additional energy term associated with the presence of finite boundaries may act to promote homogeneous nucleation and growth of dislocation loops. Based on a simplified consideration of a circular dislocation loop in a spherical nanoparticle or nanosized grain in a polycrystal, energy calculations are carried out to estimate the activation energy for homogeneous nucleation of a dislocation loop in such a system. Two different cases are considered: (1) a single nanoparticle and (2) a grain in a polycrystalline nanomaterial. Based on simulations for aluminum, it is shown that this mechanism may be plausible in both cases, albeit only for small particles and grains in the nanometer range.     

Determination of oxide in fluoride salts using an yttria-stabilized-zirconia oxygen pump

An improved method over a previous technique has been developed to determine the ppm oxide concentration of fluoride salts. The oxide is released as oxygen gas by the reaction of the test salt with potassium bromotetrafluoride at 450 °C. The molecular oxygen released is then passed through a zirconia oxygen pump which selectively removes the oxygen. The current response is recorded as a chronoamperogram, from which the ppm oxide content of the salt can be obtained. Oxygen recovery from an yttrium oxide standard was better than 99%. The precision of analysis of FLINAK was better than 13% for samples containing 110-170 ppm oxide. The LOD was 12 μg of oxygen, and the analytical range was 120 ppm to >20% for a 0.1-g sample.     

Conceptual automaticity in recognition memory: Levels-of-processing effects on familiarity.

Examined the effect of level of processing (LP) on recognition memory using 2 response-signal delays (RSD; 500 and 1500 msec). In Exp 1, LP (semantic or nonsemantic) and RSD were manipulated between 24 college students. In Exp 2, orienting task (pleasantness rating or letter judgment) and RSD were manipulated among 32 Ss. In Exp 3, study orientation and test instructions (inclusion or exclusion) were within-S factors, and RSD was a between-S factor. 32 Ss were included in Exp 3. In Exp 1, a modality effect was found for fast responses. The LP was reliable at both points in time. In Exp 2, fast responses were associated with significantly more "false-alarms" to words encoded semantically than those encoded nonsemantically. In Exp 3, both recollection and familiarity estimates were elevated by prior conceptual processing. Estimates of recollection were affected by RSD. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Maternal depressive disorder and contextual risk: contributions to the development of attachment insecurity and behavior problems in toddlerhood

Research has shown that offspring of depressed caregivers are at increased risk for maladaptive development and emotional difficulties. Specifically, infants and toddlers of depressed mothers have been shown to evidence higher percentages of insecure attachments and more behavioral difficulties than offspring of nondisordered mothers. However, even in studies that reveal significant differences between children of depressed and nondepressed caregivers, a substantial number of children with depressed caregivers do not evidence dysfunction. Such findings have resulted in increased attention to the broader social context in which children of depressed mothers develop. This investigation examined the direct influences of maternal depression on child development, as well as the role of contextual risks that may be particularly heightened in families with depressed parents. Toddlers with depressed mothers evidenced significantly more insecure attachments than did toddlers with nondisordered mothers, and this difference was not accounted for by contextual risk. In predicting child behavior problems, contextual risk was found to mediate the relation between maternal depression and child behavior problems. Father-report data on child behavior corroborated the mother report data. Results are discussed in terms of the diversity of functioning in offspring of depressed caregivers that can be attributed to varied levels of contextual risk accompanying depression.     

Production of intestinal and other tumors by 1, 2-dimethylhydrazine dihydrochloride in mice. I. A light and transmission electron microscopic study of colonic neoplasms

Single or ten weekly subcutaneous injection(s) of 1, 2-dimethylhydrazine dihydrochloride were administered separately to Swiss mice. The repeated application gave rise mainly to high incidences of tumors in the large intestine. These neoplasms occurred most frequently in the colorectal area and in cecum adjacent to ileum. Light microscopically, these lesions were classified as polypoid adenomas and adenocarcinomas. Most of the adenocarcinomas were highly invasive, although they metastasized rarely. The fine structure of the malignant cells exhibited features typical of columnar absorptive cells. A distinctive alteration was the disorderly arrangement and abnormal size and shape of the microvilli. In addition, the cells exhibited numerous free ribosomes, little RER, priminent Golgi bodies, and uniformly dispersed nuclear chromatin. Morphologically, the intestinal tumors were similar to those found in man. In addition, the repeated administration of 1, 2-DMH also induced significant incidences of neoplasms in blood vessels, lungs, anus, and kidneys while the single application produced tumors in blood vessels and liver. The main hypotheses attempting to explain the selective induction of large intestinal neoplasms are discussed.