Possible explanations for different surface quality in laser cutting with 1 micron and 10 microns beams

In laser　cutting　of　thick　steel　sheets,　quality　difference　is　observed　between　cut　surfaces　obtained　with 1 micron and 10 micron laser beams. This paper investigates physical mechanisms for this interesting and important problem of the wavelength dependence. First, striation generation process is described, based on a 3D structure of melt flow on a kerf front, which was revealed for the first time by our recent experimental observations. Two fundamental processes are suggested to explain the difference in the cut surface quality: destabilization of the melt flow in the central part of the kerf front and downward displacement of discrete melt accumulations along the side parts of the front. Then each of the processes is analyzed using a simplified analytical model. The results show that in both processes, different angular dependence of the absorptivity of the laser beam can result in the quality difference. Finally we propose use of radial polarization to improve the quality with the 1 micron wavelength

Protective copolymers for nonviral gene vectors: synthesis, vector characterization and application in gene delivery

Uncontrolled interactions of gene vectors and drug carriers in and with an in vivo environment pose serious limitations to their applicability. In order to reduce such interactions we have designed, synthesized and applied novel copolymers of poly(ethylene glycol) and reactive linkers which are derivatized with anionic peptides after copolymerization. The anionic copolymer derivatives are used to coat positively charged nonviral gene vectors by electrostatic interactions. The copolymer coat confers to polyelectrolyte colloids of DNA and polycations steric stabilization in their minimal size and prevents salt- and serum albumin-induced aggregation. Furthermore, complement activation and the interaction with serum proteins are drastically reduced or abolished in contrast to unprotected DNA complexes. The designed vectors are compatible with the intracellular steps of gene delivery and can even enhance transfection efficiency as demonstrated with various adherent and nonadherent cell lines in culture. The synthetic concept is amenable to the principles of combinatorial chemistry and the copolymeric products may be applicable beyond gene delivery in targeted drug delivery

Toward Controllable Hydraulic Coupling of Joints in a Wearable Robot

In this paper, we develop theoretical foundations for a new class of rehabilitation robot: body powered devices that route power between a user’s joints. By harvesting power from a healthy joint to assist an impaired joint, novel bimanual and self-assist therapies are enabled. This approach complements existing robotic therapies aimed at promoting recovery of motor function after neurological injury. We employ hydraulic transmissions for routing power, or equivalently for coupling the motions of a user’s joints. Fluid power routed through flexible tubing imposes constraints within a limb or between homologous joints across the body. Variable transmissions allow constraints to be steered on the fly, and simple valve switching realizes free space and locked motion. We examine two methods for realizing variable hydraulic transmissions: using valves to switch among redundant cylinders (digital hydraulics) or using an intervening electromechanical link. For both methods, we present a rigorous mathematical framework for describing and controlling the resulting constraints. Theoretical developments are supported by experiments using a prototype fluid-power exoskeleton

Self-Powered Robots to Reduce Motor Slacking During Upper-Extremity Rehabilitation: A Proof of Concept Study

Background: Robotic rehabilitation is a highly promising approach to recover lost functions after stroke or other neurological disorders. Unfortunately, robotic rehabilitation currently suffers from motor slacking , a phenomenon in which the human motor system reduces muscle activation levels and movement excursions, ostensibly to minimize metabolic- and movement-related costs. Consequently, the patient remains passive and is not fully engaged during therapy. To overcome this limitation, we envision a new class of body-powered robots and hypothesize that motor slacking could be reduced if individuals must provide the power to move their impaired limbs via their own body (i.e., through the motion of a healthy limb). Objective: To test whether a body-powered exoskeleton (i.e. robot) could reduce motor slacking during robotic training. Methods: We developed a body-powered robot that mechanically coupled the motions of the user\u27s elbow joints. We tested this passive robot in two groups of subjects (stroke and able-bodied) during four exercise conditions in which we controlled whether the robotic device was powered by the subject or by the experimenter, and whether the subject\u27s driven arm was engaged or at rest. Motor slacking was quantified by computing the muscle activation changes of the elbow flexor and extensor muscles using surface electromyography. Results: Subjects had higher levels of muscle activation in their driven arm during self-powered conditions compared to externally-powered conditions. Most notably, subjects unintentionally activated their driven arm even when explicitly told to relax when the device was self-powered. This behavior was persistent throughout the trial and did not wane after the initiation of the trial. Conclusions: Our findings provide novel evidence indicating that motor slacking can be reduced by self-powered robots; thus demonstrating promise for rehabilitation of impaired subjects using this new class of wearable system. The results also serve as a foundation to develop more sophisticated body-powered robots (e.g., with controllable transmissions) for rehabilitation purposes

Structural and magnetic properties of E-Fe_{1-x}Co_xSi thin films deposited via pulsed laser deposition

We report pulsed laser deposition synthesis and characterization of polycrystalline Fe1-xCox Si thin films on Si (111). X-ray diffraction, transmission electron, and atomic force microscopies reveal films to be dense, very smooth, and single phase with a cubic B20 crystal structure. Ferromagnetism with significant magnetic hysteresis is found for all films including nominally pure FeSi films in contrast to the very weak paramagnetism of bulk FeSi. For Fe1-xCoxSi this signifies a change from helimagnetism in bulk, to ferromagnetism in thin films. These ferromagnetic thin films are promising as a magnetic-silicide/silicon system for polarized current production, manipulation, and detection.Comment: 12 pages, 4 figures accepted in the Applied Physics Letter

Learning to walk with an adaptive gain proportional myoelectric controller for a robotic ankle exoskeleton

Abstract Background Robotic ankle exoskeletons can provide assistance to users and reduce metabolic power during walking. Our research group has investigated the use of proportional myoelectric control for controlling robotic ankle exoskeletons. Previously, these controllers have relied on a constant gain to map user’s muscle activity to actuation control signals. A constant gain may act as a constraint on the user, so we designed a controller that dynamically adapts the gain to the user’s myoelectric amplitude. We hypothesized that an adaptive gain proportional myoelectric controller would reduce metabolic energy expenditure compared to walking with the ankle exoskeleton unpowered because users could choose their preferred control gain. Methods We tested eight healthy subjects walking with the adaptive gain proportional myoelectric controller with bilateral ankle exoskeletons. The adaptive gain was updated each stride such that on average the user’s peak muscle activity was mapped to maximal power output of the exoskeleton. All subjects participated in three identical training sessions where they walked on a treadmill for 50 minutes (30 minutes of which the exoskeleton was powered) at 1.2 ms-1. We calculated and analyzed metabolic energy consumption, muscle recruitment, inverse kinematics, inverse dynamics, and exoskeleton mechanics. Results Using our controller, subjects achieved a metabolic reduction similar to that seen in previous work in about a third of the training time. The resulting controller gain was lower than that seen in previous work (β=1.50±0.14 versus a constant β=2). The adapted gain allowed users more total ankle joint power than that of unassisted walking, increasing ankle power in exchange for a decrease in hip power. Conclusions Our findings indicate that humans prefer to walk with greater ankle mechanical power output than their unassisted gait when provided with an ankle exoskeleton using an adaptive controller. This suggests that robotic assistance from an exoskeleton can allow humans to adopt gait patterns different from their normal choices for locomotion. In our specific experiment, subjects increased ankle power and decreased hip power to walk with a reduction in metabolic cost. Future exoskeleton devices that rely on proportional myolectric control are likely to demonstrate improved performance by including an adaptive gain.http://deepblue.lib.umich.edu/bitstream/2027.42/115879/1/12984_2015_Article_86.pd

Effects of CO-dark Gas on Measurements of Molecular Cloud Stability and the Size-Linewidth Relationship

Stars form within molecular clouds, so characterizing the physical states of molecular clouds is key in understanding the process of star formation. Cloud structure and stability is frequently assessed using metrics including the virial parameter and Larson (1981) scaling relationships between cloud radius, velocity dispersion, and surface density. Departures from the typical Galactic relationships between these quantities have been observed in low-metallicity environments. The amount of H$_2$ gas in cloud envelopes without corresponding CO emission is expected to be high under these conditions; therefore, this "CO-dark" gas could plausibly be responsible for the observed variations in cloud properties. We derive simple corrections that can be applied to empirical clump properties (mass, radius, velocity dispersion, surface density, and virial parameter) to account for CO-dark gas in clumps following power-law and Plummer mass density profiles. We find that CO-dark gas is not likely to be the cause of departures from Larson's relationships in low-metallicity regions, but that virial parameters may be systematically overestimated. We demonstrate that correcting for CO-dark gas is critical for accurately comparing the dynamical state and evolution of molecular clouds across diverse environments.Comment: 19 pages, 5 figures, accepted for publication in Ap

Physical conditions in the gas phases of the giant HII region LMC-N11 unveiled by Herschel - I. Diffuse [CII] and [OIII] emission in LMC-N11B

(Abridged) The Magellanic Clouds provide a nearby laboratory for metal-poor dwarf galaxies. The low dust abundance enhances the penetration of UV photons into the interstellar medium (ISM), resulting in a relatively larger filling factor of the ionized gas. Furthermore, there is likely a hidden molecular gas reservoir probed by the [CII]157um line. We present Herschel/PACS maps in several tracers, [CII], [OI]63um,145um, [NII]122um, [NIII]57um, and [OIII]88um in the HII region N11B in the Large Magellanic Cloud. Halpha and [OIII]5007A images were used as complementary data to investigate the effect of dust extinction. Observations were interpreted with photoionization models to infer the gas conditions and estimate the ionized gas contribution to the [CII] emission. Photodissociation regions (PDRs) are probed through polycyclic aromatic hydrocarbons (PAHs). We first study the distribution and properties of the ionized gas. We then constrain the origin of [CII]157um by comparing to tracers of the low-excitation ionized gas and of PDRs. [OIII] is dominated by extended emission from the high-excitation diffuse ionized gas; it is the brightest far-infrared line, ~4 times brighter than [CII]. The extent of the [OIII] emission suggests that the medium is rather fragmented, allowing far-UV photons to permeate into the ISM to scales of >30pc. Furthermore, by comparing [CII] with [NII], we find that 95% of [CII] arises in PDRs, except toward the stellar cluster for which as much as 15% could arise in the ionized gas. We find a remarkable correlation between [CII]+[OI] and PAH emission, with [CII] dominating the cooling in diffuse PDRs and [OI] dominating in the densest PDRs. The combination of [CII] and [OI] provides a proxy for the total gas cooling in PDRs. Our results suggest that PAH emission describes better the PDR gas heating as compared to the total infrared emission.Comment: Accepted for publication in Astronomy and Astrophysics. Fixed inverted line ratio in Sect. 5.

Fragmentation Instability of Molecular Clouds: Numerical Simulations

We simulate fragmentation and gravitational collapse of cold, magnetized molecular clouds. We explore the nonlinear development of an instability mediated by ambipolar diffusion, in which the collapse rate is intermediate to fast gravitational collapse and slow quasistatic collapse. Initially uniform stable clouds fragment into elongated clumps with masses largely determined by the cloud temperature, but substantially larger than the thermal Jeans mass. The clumps are asymmetric, with significant rotation and vorticity, and lose magnetic flux as they collapse. The clump shapes, intermediate collapse rates, and infall profiles may help explain observations not easily fit by contemporary slow or rapid collapse models.Comment: 25pp, 20 small eps figures, in press ApJ, April 1, 200

Isolation and Antibacterial Activity Test of Seagrass Epiphytic Symbiont Bacteria Thalassia hemprichii from Bahowo Waters, North Sulawesi

Seagrass is a higher plant and has the ability to produce bioactive compounds such as antibacterial. Seagrass is also a host to a variety of bacteria. Bacteria that live in the host will produce the same compounds as the host's body. The utilization of symbiotic bacteria with seagrasses as producers of bioactive compounds such as antibacterial can be used as a solution to reduce excessive seagrass uptake in nature. On the other hand, bacteria have the advantage of being fast and easy to grow and can be mass-produced and more economical. This study aims to isolate and test the antibacterial activity of the epiphytic bacteria of seagrass symbionts. Epiphytic bacteria of seagrass symbionts were grown on Nutrient Agar media directly in the field and bacterial isolation was carried out based on the morphological characteristics of the bacterial isolates. The antibacterial activity test was carried out using the disc method with the test bacteria Stapylococcus aureus, Streptococcus mutans, Escherichia coli, Salmonella thypi, and antibiotics as positive controls. The ability of bacteria to produce antibacterial was indicated by the formation of an inhibition zone around the paper disc containing the epiphytic bacteria of the seagrass symbiont T. hemprichii. A total of 3 isolates of epiphytic bacteria were isolated from T. hemprichii seagrass from Bahowo Waters, Tongkaina Village, Bunaken District, these isolates are namely Epifit 1, Epiphyte 2, and Epiphyte 3. Epiphyte 2 isolate had antibacterial activity against S. mutans, S. aureus, and S. thypi test bacteria, Epiphyte 3 isolate had antibacterial activity against S. mutans, and S. thypi test bacteria.Key words: Bacteria; Antibacterial; T. hemprichii; symbionts; BahowoAbstrakLamun merupakan tumbuhan tingkat tinggi dan memiliki kemampuan menghasilkan senyawa  bioaktif seperti antibakteri. Lamun juga merupakan tempat hidup atau inang dari berbagai bakteri. Bakteri yang hidup pada inang akan menghasilkan senyawa yang sama dengan tubuh inangnya. Pemanfaatan bakteri yang bersimbiosis dengan lamun sebagai produsen senyawa bioaktif seperti antibakteri dapat dijadikan sebagai solusi dalam mengurangi pengambilan lamun yang berlebihan di alam. Dilain pihak, bakteri memiliki keunggulan karena pertumbuhan bakteri yang cepat dan mudah tumbuh, dapat diproduksi secara massal dan lebih ekonomis. Penelitian ini bertujuan untuk mengisolasi dan menguji aktivitas antibakteri dari bakteri epifit simbion lamun T. hemprichii dari Perairan Bahowo.  Bakteri epifit simbion lamun ditumbuhkan pada media NA secara langsung di lapangan dan isolasi bakteri dilaksanakan berdasarkan karateristik morfologi isolat bakteri. Uji aktivitas bakteri dilakukan menggunakan metode cakram dengan bakteri uji S. aureus, S. mutans, E. coli, dan S. thypi dan antibiotik sebagai kontrol positif. Kemampuan bakteri menghasilkan antibakteri ditandai dengan terbentuknya zona hambat disekitar kertas cakram yang mengandung bakkteri epifit simbion lamun T. hemprichii.  Sebanyak 3 isolat bakteri epifit berhasil diisolasi pada lamun T. hemprichii dari Perairan Bahowo, Kelurahan Tongkaina, Kecamatan Bunaken yaitu Epifit 1, Epifit 2, dan Epifit 3. Isolat epifit 3 memiliki aktivitas antibakteri terhadap bakteri uji S. thypi, isolat Epifit 2 terhadap bakteri uji S. mutans, S. aureus, dan S. thypi, isolat Epifit 3 terhadap bakteri uji S. mutans, dan S. thypi.Kata kunci: Bakteri; Antibakteri; T. hemprichii; Simbion; Bahow