An analytical approach to sorting in periodic and random potentials

There has been a recent revolution in the ability to manipulate micrometer-sized objects on surfaces patterned by traps or obstacles of controllable configurations and shapes. One application of this technology is to separate particles driven across such a surface by an external force according to some particle characteristic such as size or index of refraction. The surface features cause the trajectories of particles driven across the surface to deviate from the direction of the force by an amount that depends on the particular characteristic, thus leading to sorting. While models of this behavior have provided a good understanding of these observations, the solutions have so far been primarily numerical. In this paper we provide analytic predictions for the dependence of the angle between the direction of motion and the external force on a number of model parameters for periodic as well as random surfaces. We test these predictions against exact numerical simulations.

Giant acceleration of free diffusion by use of titled periodic potentials

The effective diffusion coefficient for the overdamped Brownian motion in a tilted periodic potential is calculated in closed analytical form. Universality classes and scaling properties for weak thermal noise are identified near the threshold tilt where deterministic running solutions set in. In this regime the diffusion may be greatly enhanced, as compared to free thermal diffusion with, for a realistic experimental setup, an enhancement of up to 14 orders of magnitude.

A CT-based study investigating the relationship between pedicle screw placement and stimulation threshold of compound muscle action potentials measured by intraoperative neurophysiological monitoring.

PURPOSE: Neurophysiological monitoring aims to improve the safety of pedicle screw placement, but few quantitative studies assess specificity and sensitivity. In this study, screw placement within the pedicle is measured (post-op CT scan, horizontal and vertical distance from the screw edge to the surface of the pedicle) and correlated with intraoperative neurophysiological stimulation thresholds. METHODS: A single surgeon placed 68 thoracic and 136 lumbar screws in 30 consecutive patients during instrumented fusion under EMG control. The female to male ratio was 1.6 and the average age was 61.3 years (SD 17.7). Radiological measurements, blinded to stimulation threshold, were done on reformatted CT reconstructions using OsiriX software. A standard deviation of the screw position of 2.8 mm was determined from pilot measurements, and a 1 mm of screw-pedicle edge distance was considered as a difference of interest (standardised difference of 0.35) leading to a power of the study of 75 % (significance level 0.05). RESULTS: Correct placement and stimulation thresholds above 10 mA were found in 71 % of screws. Twenty-two percent of screws caused cortical breach, 80 % of these had stimulation thresholds above 10 mA (sensitivity 20 %, specificity 90 %). True prediction of correct position of the screw was more frequent for lumbar than for thoracic screws. CONCLUSION: A screw stimulation threshold of >10 mA does not indicate correct pedicle screw placement. A hypothesised gradual decrease of screw stimulation thresholds was not observed as screw placement approaches the nerve root. Aside from a robust threshold of 2 mA indicating direct contact with nervous tissue, a secondary threshold appears to depend on patients' pathology and surgical conditions.

Soil Water Potentials and Capsicum annuum L. under Salinity

ABSTRACT Investigations into water potentials in the soil-plant system are of great relevance in environments with abiotic stresses, such as salinity and drought. An experiment was developed using bell pepper in a Neossolo Flúvico (Fluvent) irrigated with water of six levels of electrical conductivity (0, 1, 3, 5, 7 and 9 dS m-1) by using exclusively NaCl and by simulating the actual condition (using a mixture of salts). The treatments were arranged in a randomized block design, in a 6 × 2 factorial arrangement, with four replicates. Soil matric (Ψm) and osmotic (Ψo) potentials were determined 70 days after transplanting (DAT). Soil total potential was considered as the sum of Ψm and Ψo. Leaf water (obtained with the Scholander Chamber) and osmotic potentials were determined before sunrise (predawn) and at noon at 42 and 70 DAT. There were no significant differences between the salt sources used in the irrigation water for soil and plant water potentials. The supply of salts to the soil through irrigation water was the main factor responsible for the decrease in Ψo in the soil and in bell pepper leaves. The total potential of bell pepper at predawn reached values of -1.30 and -1.33 MPa at 42 and 70 DAT, respectively, when water of 9 dS m-1 was used in the irrigation. The total potential at noon reached -2.19 MPa. The soil subjected to the most saline treatment reached a water potential of -1.20 MPa at 70 DAT. There was no predawn equilibrium between the total water potentials of the soil and the plant, indicating that soil potential cannot be considered similar to that of the plant. The determination of the osmotic potential in the soil solution should not be neglected in saline soils, since it has strong influence on the calculation of the total potential.

Partition coefficient and molecular flexibility: the concept of lipophilicity space.

The rationale of this study was to investigate molecular flexibility and its influence on physicochemical properties with a view to uncovering additional information on the fuzzy concept of dynamic molecular structure. Indeed, it is now known that computed molecular interaction fields (MIFs) such as molecular electrostatic potentials (MEPs) and lipophilicity potentials (MLPs) are conformation-dependent, as are dipole moments. A database of 125 compounds was used whose conformational space was explored, while conformation-dependent parameters were computed for each non-redundant conformer found in the conformational space of the compounds. These parameters were the virtual log P (log P(MLP), calculated by a MLP approach), the apolar surface area (ASA), polar surface area (PSA), and solvent-accessible surface (SAS). For each compound, the range taken by each parameter (its property space) was divided by the number of rotors taken as an index of flexibility, yielding a parameter termed 'molecular sensitivity'. This parameter was poorly correlated with others (i.e., it contains novel information) and showed the compounds to fall into two broad classes. 'Sensitive' molecules are those whose computed property ranges are markedly sensitive to conformational effects, whereas 'insensitive' (in fact, less sensitive) molecules have property ranges which are comparatively less affected by conformational fluctuations. A pharmacokinetic application is presented.

Avaliação do acesso a periódicos eletrônicos na web pela análise do arquivo de log de acesso

Este artigo apresenta uma abordagem sobre a avaliação do acesso a periódicos eletrônicos disponibilizados na World Wide Web por meio da análise do arquivo de log de acesso. O arquivo de log de acesso da revista Informação & Sociedade: Estudos é processado e apresentado como um exemplo de aplicação do uso de uma ferramenta automatizada de análise para arquivo de iog de acesso. As características inerentes à análise do arquivo de log de acesso são apresentadas e discutidas.

Age-related differences on event-related potentials and brain rhythm oscillations during working memory activation.

Previous functional imaging studies have pointed to the compensatory recruitment of cortical circuits in old age in order to counterbalance the loss of neural efficiency and preserve cognitive performance. Recent electroencephalographic (EEG) analyses reported age-related deficits in the amplitude of an early positive-negative working memory (PN(wm)) component as well as changes in working memory (WM)-load related brain oscillations during the successful performance of the n-back task. To explore the age-related differences of EEG activation in the face of increasing WM demands, we assessed the PN(wm) component area, parietal alpha event-related synchronization (ERS) as well as frontal theta ERS in 32 young and 32 elderly healthy individuals who successfully performed a highly WM demanding 3-back task. PN(wm) area increased with higher memory loads (3- and 2-back > 0-back tasks) in younger subjects. Older subjects reached the maximal values for this EEG parameter during the less WM demanding 0-back task. They showed a rapid development of an alpha ERS that reached its maximal amplitude at around 800 ms after stimulus onset. In younger subjects, the late alpha ERS occurred between 1,200 and 2,000 ms and its amplitude was significantly higher compared with elders. Frontal theta ERS culmination peak decreased in a task-independent manner in older compared with younger cases. Only in younger individuals, there was a significant decrease in the phasic frontal theta ERS amplitude in the 2- and 3-back tasks compared with the detection and 0-back tasks. These observations suggest that older adults display a rapid mobilization of their neural generators within the parietal cortex to manage very low demanding WM tasks. Moreover, they are less able to activate frontal theta generators during attentional tasks compared with younger persons.

Self-potentials in partially saturated media: the importance of explicit modeling of electrode effects

Self-potential (SP) data are of interest to vadose zone hydrology because of their direct sensitivity to water flow and ionic transport. There is unfortunately little consensus in the literature about how to best model SP data under partially saturated conditions, and different approaches (often supported by one laboratory data set alone) have been proposed. We argue that this lack of agreement can largely be traced to electrode effects that have not been properly taken into account. A series of drainage and imbibition experiments were considered in which we found that previously proposed approaches to remove electrode effects were unlikely to provide adequate corrections. Instead, we explicitly modeled the electrode effects together with classical SP contributions using a flow and transport model. The simulated data agreed overall with the observed SP signals and allowed decomposing the different signal contributions to analyze them separately. After reviewing other published experimental data, we suggest that most of them include electrode effects that have not been properly taken into account. Our results suggest that previously presented SP theory works well when considering the modeling uncertainties presently associated with electrode effects. Additional work is warranted to not only develop suitable electrodes for laboratory experiments but also to assure that associated electrode effects that appear inevitable in longer term experiments are predictable, so that they can be incorporated into the modeling framework.

Effects of muscle fibre shortening on the characteristics of surface motor unit potentials.

Traditionally, studies dealing with muscle shortening have concentrated on assessing its impact on conduction velocity, and to this end, electrodes have been located between the end-plate and tendon regions. Possible morphologic changes in surface motor unit potentials (MUPs) as a result of muscle shortening have not, as yet, been evaluated or characterized. Using a convolutional MUP model, we investigated the effects of muscle shortening on the shape, amplitude, and duration characteristics of MUPs for different electrode positions relative to the fibre-tendon junction and for different depths of the MU in the muscle (MU-to-electrode distance). It was found that the effects of muscle shortening on MUP morphology depended not only on whether the electrodes were between the end-plate and the tendon junction or beyond the tendon junction, but also on the specific distance to this junction. When the electrodes lie between the end-plate and tendon junction, it was found that (1) the muscle shortening effect is not important for superficial MUs, (2) the sensitivity of MUP amplitude to muscle shortening increases with MU-to-electrode distance, and (3) the amplitude of the MUP negative phase is not affected by muscle shortening. This study provides a basis for the interpretation of the changes in MUP characteristics in experiments where both physiological and geometrical aspects of the muscle are varied.

Long-term impacts of forest harvesting related soil disturbance on log product yields and economic potential in a New Zealand forest

Abstract

A tutorial review of electrical neuroimaging from group-average to single-trial event-related potentials.

This tutorial review details some of the recent advances in signal analyses applied to event-related potential (ERP) data. These "electrical neuroimaging" analyses provide reference-independent measurements of response strength and response topography that circumvent statistical and interpretational caveats of canonical ERP analysis methods while also taking advantage of the greater information provided by high-density electrode montages. Electrical neuroimaging can be applied across scales ranging from group-averaged ERPs to single-subject and single-trial datasets. We illustrate these methods with a tutorial dataset and place particular emphasis on their suitability for studies of clinical and/or developmental populations.

Vertical Clearance Restrictions on Primary Roads and Primary Road Extensions: Standard U.S. Measurements [Vertical Clearance Log], May 1, 2015

The Vertical Clearance Log is prepared for the purpose of providing vertical clearance restrictions by route on the primary road system. This report is used by the Iowa Department of Transportation’s Motor Carrier Services to route oversize vehicles around structures with vertical restrictions too low for the cargo height. The source of the data is the Geographic Information Management System (GIMS) that is managed by the Office of Research & Analytics in the Performance & Technology Division. The data is collected by inspection crews and through the use of LiDAR technology to reflect changes to structures on the primary road system. This log is produced annually.

The attractiveness of the work is affected when production of handcrafted log houses moves indoors

Abstract