Two-frequency acousto-optic modulator driver to improve the beam pointing stability during intensity ramps

We report on a scheme to improve the pointing stability of the first order beam diffracted by an acousto-optic modulator (AOM). Due to thermal effects inside the crystal, the angular position of the beam can change by as much as 1 mrad when the radio-frequency power in the AOM is reduced to decrease the first order beam intensity. This is done, for example, to perform forced evaporative cooling in ultracold atom experiments using far-off-resonant optical traps. We solve this problem by driving the AOM with two radio frequencies f(1) and f(2). The power of f(2) is adjusted relative to the power of f(1) to keep the total power constant. Using this, the beam displacement is decreased by a factor of 20. The method is simple to implement in existing experimental setups, without any modification of the optics.     

Analysis of commercial anhydrous tetrasodium pyrophosphate

A titration method of analysis is given for Na₄P₂O₇ in commercial anhydrous tetrasodium pyrophosphate using a modification of the Britske and Dragunov titration method. In the absence of other polyphosphates, a degree of precision is obtained satisfactory for the type of product supplied by the manufacturers. Time required for analysis is much less than for methods relying upon precipitation with subsequent gravimetric treatment. Results of cooperative work are given. During 1939 Committee D-12 on Soaps and Other Detergents of A. S. T. M. formulated specifications for tetrasodium pyrophosphate (anhydrous) which now appear as their specification D 595-42 T. The subcommittee on Analysis of Special Detergents was asked to provide a method of analysis of reasonable accuracy for use on commercial material containing about 95 to 100% Na₄P₂O₇. A search of the literature suggested several possible methods (1,2,3) and various modifications supplied by interested laboratories were considered. Cooperative work was carried out by ten laboratories with the result that the following modification of the Britske and Dragunov method (2) was adopted as a Tentative Standard of the A. S. T. M. (4) in 1941 and has just recently been advanced to Standard. The procedure describes an indirect determination of tetrasodium pyrophosphate by titration of the sulfuric acid liberated by the action of zinc sulfate on an acid pyrophosphate in accordance with the following reactions:

$$\begin{gathered} Na_4 P_2 O_7 + 2HCl = Na_2 H_2 P_2 O_7 + 2NaCl \hfill \\ Na_2 H_2 P_2 O_7 + 2ZnSO_4 = Zn_2 P_2 O_7 + Na_2 SO_4 + \hfill \\ H_2 SO_4 \hfill \\ \end{gathered}$$     

Evaluating distance-based clustering for user (browse and click) sessions in a domain-specific collection

We seek to improve information retrieval in a domain-specific collection by clustering user sessions from a click log and then classifying later user sessions in real time. As a preliminary step, we explore the main assumption of this approach: whether user sessions in such a site are related to the question that they are answering. Since a large class of machine learning algorithms use a distance measure at the core, we evaluate the suitability of common machine learning distance measures to distinguish sessions of users searching for the answer to same or different questions. We found that two distance measures work very well for our task and three others do not. As a further step, we then investigate how effective the distance measures are when used in clustering. For our dataset, we conducted a user study where we had multiple users answer the same set of questions. This data, grouped by question, was used as our gold standard for evaluating the clusters produced by the clustering algorithms. We found that the observed difference between the two classes of distance measures affected the quality of the clusterings, as expected. We also found that one of the two distance measures that worked well to differentiate sessions, worked significantly better than the other when clustering. Finally, we discuss why some distance metrics performed better than others in the two parts of our work.     

Cellular internalization of enhanced green fluorescent protein ligated to a human calcitonin-based carrier peptide

Carrier peptides offer new opportunities to overcome problems in cellular drug delivery. Their objectives are improved cellular uptake or permeation of biological membranes, which are important pharmacokinetic features for the cellular distribution of therapeutics. Previously, human calcitonin (hCT) and selected C-terminal hCT fragments have been shown to be internalized and to permeate the epithelium of the nasal mucosa. To assess the potential of hCT-derived carrier peptides for cellular internalization of a model protein we fused enhanced green fluorescent protein (EGFP) and the [C(8)]hCT8-32 fragment by using expressed protein ligation (EPL). EGFP thioester was obtained by intein-mediated purification with an affinity chitin-binding tag (the IMPACT system, based on protein splicing). Internalization of EGFP-[C(8)]hCT8-32 by excised bovine nasal mucosa was monitored by confocal laser scanning microscopy. This novel conjugate displayed internalization into some sectors of the mucosa, whereas EGFP itself was not capable of translocation. Thus, we demonstrate successful internalization of a model protein through ligation to an hCT-derived carrier peptide, which has potential for the delivery of therapeutics. At this point the respective mechanism of translocation is unknown.     

ω‐Imidazolyl‐ and ω‐Tetrazolylalkylcarbamates as Inhibitors of Fatty Acid Amide Hydrolase: Biological Activity and in vitro Metabolic Stability

Fatty acid amide hydrolase (FAAH) is a serine hydrolase that terminates the analgesic and anti‐inflammatory effects of endocannabinoids such as anandamide. Herein, structure–activity relationship studies on a new series of aryl N‐(ω‐imidazolyl‐ and ω‐tetrazolylalkyl)carbamate inhibitors of FAAH were investigated. As one result, a pronounced increase in inhibitory potency was observed if a phenyl residue attached to the carbamate oxygen atom was replaced by a pyridin‐3‐yl moiety. The most active compounds exhibited IC₅₀ values in the low nanomolar range. In addition, investigations on the metabolic properties of these inhibitors were performed. In rat liver homogenate and in porcine plasma, the extent of their degradation was shown to be strongly dependent on the kind of aryl residue bound to the carbamate as well as on the length and type of the alkyl spacer connecting the carbamate group with the heterocyclic system. With the aid of esterase inhibitors it was shown that in porcine plasma, carboxylesterase‐like enzymes and paraoxonase are involved in carbamate cleavage. Moreover, it was found that highly active pyridin‐3‐yl carbamates reacted with albumin, which led to covalent albumin adducts.     

Projected potential profiles across interfaces obtained by reconstructing the exit face wave function from through focal series

An iterative method for reconstructing the exit face wave function from a through focal series of transmission electron microscopy image line profiles across an interface is presented. Apart from high-resolution images recorded with small changes in defocus, this method works also well for a large defocus range as used for Fresnel imaging. Using the phase-object approximation the projected electrostatic as well as the absorptive potential profiles across an interface are determined from this exit face wave function. A new experimental image alignment procedure was developed in order to align images with large relative defocus shift. The performance of this procedure is shown to be superior to other image alignment procedures existing in the literature. The reconstruction method is applied to both simulated and experimental images.     

Where do university graduates live? – A computer vision approach using satellite images

In this article, we examine to what extent the settlement of university graduates can be derived from satellite images. We apply a convolutional neural network (CNN) to grid images of a city and predict five density classes of university graduates at a micro level (250 m × 250 m grid size). The CNN reaches an accuracy rate of 40.5% (random approach: 20%). Furthermore, the accuracy increases to 78.3% when considering a one-class deviation compared to the true class. We also examine the predictability of inhabited and uninhabited grid cells, where we achieve an accuracy of 95.3% using the same CNN. From this, we conclude that there is information that correlates with graduate density that can be derived by analysing only satellite images. The findings show the high potential of computer vision for urban and regional economics. Particularly in data-poor regions, the approach utilised facilitates comparative analytics and provides a possible solution for the modifiable aerial unit (MAU) problem. The MAU problem is a statistical bias that can influence the results of a spatial data analysis of point-estimate data that is aggregated in districts of different shapes and sizes, distorting the results.

     

Analog hardware for detecting discontinuities in early vision

The detection of discontinuities in motion, intensity, color, and depth is a well-studied but difficult problem in computer vision [6]. We discuss the first hardware circuit that explicitly implements either analog or binary line processes in a deterministic fashion. Specifically, we show that the processes of smoothing (using a first-order or membrane type of stabilizer) and of segmentation can be implemented by a single, two-terminal nonlinear voltage-controlled resistor, the resistive fuse; and we derive its current-voltage relationship from a number of deterministic approximations to the underlying stochastic Markov random fields algorthms. The concept that the quadratic variation functionals of early vision can be solved via linear resistive networks minimizing power dissipation [37] can be extended to non-convex variational functionals with analog or binary line processes being solved by nonlinear resistive networks minimizing the electrical co-content.We have successfully designed, tested, and demonstrated an analog CMOS VLSI circuit that contains a 1D resistive network of fuses implementing piecewise smooth surface interpolation. We furthermore demonstrate the segmenting abilities of these analog and deterministic line processes by numerically simulating the nonlinear resistive network computing optical flow in the presence of motion discontinuities. Finally, we discuss various circuit implementations of the optical flow computation using these circuits.     

2D Vector field approximation using linear neighborhoods

We present a vector field approximation for two-dimensional vector fields that preserves their topology and significantly reduces the memory footprint. This approximation is based on a segmentation. The flow within each segmentation region is approximated by an affine linear function. The implementation is driven by four aims: (1) the approximation preserves the original topology; (2) the maximal approximation error is below a user-defined threshold in all regions; (3) the number of regions is as small as possible; and (4) each point has the minimal approximation error. The generation of an optimal solution is computationally infeasible. We discuss this problem and provide a greedy strategy to efficiently compute a sensible segmentation that considers the four aims. Finally, we use the region-wise affine linear approximation to compute a simplified grid for the vector field.