Single-frequency, high-power, continuous-wave fiber-laser-pumped Ti:sapphire laser

We demonstrate a high-power, continuous-wave (cw), single-frequency green source based on single-pass second-harmonic generation of a Yb-fiber laser in MgO:sPPLT as a viable pump source for a cw single-frequency Ti:sapphire ring laser. By careful design and optimization, the Ti:sapphire laser can provide as much as 2.3 W of cw single-frequency output across a 47 nm tuning range, limited by the reflectivity of the cavity mirrors. By implementing active stabilization of the laser frequency to an external reference, an ultrastable Fabry-Perot interferometer, we obtain a frequency stability better than 12 MHz over 10 min and continuous tunability greater than 180 MHz. Stable output power with peak-to-peak fluctuation of 5.4% over 75 min, in high spatial beam quality with M(2)<1.34, is achieved.     

Materials Issues Related to Catalysts for Treatment of Diesel Exhaust

The driver for lean NO _x treatment is the need to meet regulatory standards for diesel engines and gasoline direct injection spark-ignited engines that offer better fuel economy. Efforts over the last decade have been focused toward finding an active lean NO _x catalyst that can reduce NO _x under oxidizing conditions or strategies such as selective catalytic reduction (SCR), plasma-catalysis, plasma catalyst SCR, and lean NO _x traps with varying degrees of success. At present, it appears that SCR with urea and lean NO _x traps are the leading contender technologies for commercial deployment. Key issues that remain to be resolved for these two technologies include byproduct formation, dosing control, and durability. In this review, we summarize material-related issues that are unique to each of these technologies, and point out the improvements necessary to facilitate their deployment.     

Capillary electrophoresis separation in the presence of an immiscible boundary for droplet analysis

This paper demonstrates the ability to use capillary electrophoresis (CE) separation coupled with laser-induced fluorescence for analyzing the contents of single femtoliter-volume aqueous droplets. A single droplet was formed using a T-channel (3 microm wide by 3 microm tall) connected to microinjectors, and then the droplet was fluidically moved to an immiscible boundary that isolates the CE channel (50 microm wide by 50 microm tall) from the droplet generation region. Fusion of the aqueous droplet with the immiscible boundary effectively injects the droplet content into the separation channel. In addition to injecting the contents of droplets, we found aqueous samples can be introduced directly into the separation channel by reversibly penetrating and resealing the immiscible partition. Because droplet generation in channels requires hydrophobic surfaces, we have also investigated the advantages to using all hydrophobic channels versus channel systems with patterned hydrophobic and hydrophilic regions. To fabricate devices with patterned surface chemistry, we have developed a simple strategy based on differential wetting to deposit selectively a hydrophilic polymer (poly(styrenesulfonate)) onto desired regions of the microfluidic chip. Finally, we applied our device to the separation of a simple mixture of fluorescein-labeled amino acids contained within a approximately 10-fL droplet.     

Robot-assisted shopping for the blind: issues in spatial cognition and product selection

Research on spatial cognition and blind navigation suggests that a device aimed at helping blind people to shop independently should provide the shopper with effective interfaces to the locomotor and haptic spaces of the supermarket. In this article, we argue that robots can act as effective interfaces to haptic and locomotor spaces in modern supermarkets. We also present the design and evaluation of three product selection modalities—browsing, typing and speech, which allow the blind shopper to select the desired product from a repository of thousands of products.     

Supine and prone colon registration using quasi-conformal mapping

In virtual colonoscopy, CT scans are typically acquired with the patient in both supine (facing up) and prone (facing down) positions. The registration of these two scans is desirable so that the user can clarify situations or confirm polyp findings at a location in one scan with the same location in the other, thereby improving polyp detection rates and reducing false positives. However, this supine-prone registration is challenging because of the substantial distortions in the colon shape due to the patient's change in position. We present an efficient algorithm and framework for performing this registration through the use of conformal geometry to guarantee that the registration is a diffeomorphism (a one-to-one and onto mapping). The taeniae coli and colon flexures are automatically extracted for each supine and prone surface, employing the colon geometry. The two colon surfaces are then divided into several segments using the flexures, and each segment is cut along a taenia coli and conformally flattened to the rectangular domain using holomorphic differentials. The mean curvature is color encoded as texture images, from which feature points are automatically detected using graph cut segmentation, mathematic morphological operations, and principal component analysis. Corresponding feature points are found between supine and prone and are used to adjust the conformal flattening to be quasi-conformal, such that the features become aligned. We present multiple methods of visualizing our results, including 2D flattened rendering, corresponding 3D endoluminal views, and rendering of distortion measurements. We demonstrate the efficiency and efficacy of our registration method by illustrating matched views on both the 2D flattened colon images and in the 3D volume rendered colon endoluminal view. We analytically evaluate the correctness of the results by measuring the distance between features on the registered colons.     

Approximability of the Firefighter Problem

We provide approximation algorithms for several variants of the Firefighter problem on general graphs. The Firefighter problem models the case where a diffusive process such as an infection (or an idea, a computer virus, a fire) is spreading through a network, and our goal is to contain this infection by using targeted vaccinations. Specifically, we are allowed to vaccinate at most a fixed number (called the budget) of nodes per time step, with the goal of minimizing the effect of the infection. The difficulty of this problem comes from its temporal component, since we must choose nodes to vaccinate at every time step while the infection is spreading through the network, leading to notions of “cuts over time”. We consider two versions of the Firefighter problem: a “non-spreading” model, where vaccinating a node means only that this node cannot be infected; and a “spreading” model where the vaccination itself is an infectious process, such as in the case where the infection is a harmful idea, and the vaccine to it is another infectious beneficial idea. We look at two measures: the MaxSave measure in which we want to maximize the number of nodes which are not infected given a fixed budget, and the MinBudget measure, in which we are given a set of nodes which we have to save and the goal is to minimize the budget. We study the approximability of these problems in both models.     

Discovery of Halogenated Benzothiadiazine Derivatives with Anticancer Activity**

Mitochondrial respiratory complex II (CII), also known as succinate dehydrogenase, plays a critical role in mitochondrial metabolism. Known but low potency CII inhibitors are selectively cytotoxic to cancer cells including the benzothiadiazine-based anti-hypoglycemic diazoxide. Herein, we study the structure-activity relationship of benzothiadiazine derivatives for CII inhibition and their effect on cancer cells for the first time. A 15-fold increase in CII inhibition was achieved over diazoxide, albeit with micromolar IC₅₀ values. Cytotoxicity evaluation of the novel derivatives resulted in the identification of compounds with much greater antineoplastic effect than diazoxide, the most potent of which possesses an IC₅₀ of 2.93±0.07 μM in a cellular model of triple-negative breast cancer, with high selectivity over nonmalignant cells and more than double the potency of the clinical agent 5-fluorouracil. No correlation between cytotoxicity and CII inhibition was found, thus indicating an as-yet-undefined mechanism of action of this scaffold. The derivatives described herein represent valuable hit compounds for therapeutic discovery in triple-negative breast cancer.     

Synthesis and electrical properties of cubic NaxWO3 thin films across the metal-insulator transition

Highly oriented (1 0 0) Na_xWO₃ thin films were fabricated in the composition range 0.1 ≤ x ≤ 0.46 by pulsed laser deposition technique. The films showed transition from metallic to insulating behaviour at a critical composition between x = 0.15 and 0.2. The pseudo-cubic symmetry of Na_xWO₃ thin films across the transition region is desirable for understanding the composition controlled metal-insulator transition in the absence of any structural phase transformation. The electrical transport properties exhibited by these films across the transition regime were investigated. While the resistivity varied as T² at low temperatures in the metallic regime, a variable range hopping conduction was observed for the insulating samples. For metallic compositions, a non-linear dependence of resistivity in temperature was also observed from 300 to 7 K, whose exponent varied with the composition of the film.     

Sharing and caring of eScience data

This commentary reflects on the issues presented in this volume from the perspective of a large eScience project, GEON, whose aim is to promote data integration in the geosciences within the US and abroad. Technical, social, and regulatory challenges accompanying the collection, curation, and sharing of eScience data are discussed. Opportunities and barriers to engaging in international eScience collaborations are highlighted.