The potential of electron beam radiation for simultaneous surface modification and bioresorption control of PLLA

Bioresorbable polymers have been widely investigated as materials exhibiting significant potential for successful application in the fields of tissue engineering and drug delivery. Further to the ability to control degradation, surface engineering of polymers has been highlighted as a key method central to their development. Previous work has demonstrated the ability of electron beam (e-beam) technology to control the degradation profiles and bioresorption of a number of commercially relevant bioresorbable polymers (poly-l-lactic acid (PLLA), Llactide/DL-lactide co-polymer (PLDL) and poly(lactic-co-glycolic acid (PLGA)). This work investigates the further potential of ebeam technology to impart added biofunctionality through the manipulation of polymer (PLLA) surface properties. PLLA samples were subjected to e-beam treatments in air, with varying beam energies and doses. Surface characterization was then performed using contact angle analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy. Results demonstrated a significant increase in surface wettability post e-beam treatment. In correlation with this, XPS data showed the introduction of oxygen-containing functional groups to the surface of PLLA. Raman spectroscopy indicated chain scission in the near surface region of PLLA (as predicted). However, e-beam effects on surface properties were not shown to be dependent on beam energy or dose. E-beam irradiation did not seem to affect the surface roughness of PLLA as a direct consequence of the treatment.

A bit-level systolic architecture for implementing a VQ tree search

A bit-level systolic array system for performing a binary tree Vector Quantization codebook search is described. This consists of a linear chain of regular VLSI building blocks and exhibits data rates suitable for a wide range of real-time applications. A technique is described which reduces the computation required at each node in the binary tree to that of a single inner product operation. This method applies to all the common distortion measures (including the Euclidean distance, the Weighted Euclidean distance and the Itakura-Saito distortion measure) and significantly reduces the hardware required to implement the tree search system. © 1990 Kluwer Academic Publishers.

Algorithmic method for scraper load-time optimization

Scrapers have established an important position in the earthmoving field as they are independently capable of accomplishing an earthmoving operation. Given that loading a scraper to its capacity does not entail its maximum production, optimizing the scraper’s loading time is an essential prerequisite for successful operations management. The relevant literature addresses the loading time optimization through a graphical method that is founded on the invalid assumption that the hauling time is independent of the load time. To correct this, a new algorithmic optimization method that incorporates the golden section search and the bisection algorithm is proposed. Comparison of the results derived from the proposed and the existing method demonstrates that the latter entails the systematic needless prolongation of the loading stage thus resulting in reduced hourly production and increased cost. Therefore, the proposed method achieves an improved modeling of scraper earthmoving operations and contributes toward a more efficient cost management.

Mask assisted fabrication of nanoislands of BiFeO3 by ion beam milling

We report on a low-damage method for direct and rapid fabrication of arrays of epitaxial BiFeO3(BFO) nanoislands. An array of aluminium dots is evaporated through a stencil mask on top of an epitaxial BiFeO3 thin film. Low energy focused ion beam milling of an area several microns wide containing the array-covered film leads to removal of the bismuth ferrite in between the aluminium-masked dots. By chemical etching of the remaining aluminium, nanoscale epitaxial bismuth ferrite islands with diameter ∼250 nm were obtained. Piezoresponse force microscopy showed that as-fabricated structures exhibited good piezoelectric and ferroelectric properties, with polarization state retention of several days.

Electron-acoustic solitons in an electron-beam plasma system with kappa-distributed electrons

Interaction of a stream of high-energy electrons with the background plasma plays an important role in the astrophysical phenomena such as interplanetary and stellar bow shock and Earth's foreshock emission. It is not yet fully understood how electrostatic solitary waves are produced at the bow shock. Interestingly, a population of energetic suprathermal electrons were also found to exist in those environments. Previously, we have studied the properties of negative electrostatic potential solitary structures exist in such a plasma with excess suprathermal electrons. In the present study, we investigate the existence conditions and propagation properties of electron-acoustic solitary waves in a plasma consisting of an electron beam fluid, a cold electron fluid, and hot suprathermal electrons modeled by a kappa-distribution function. The Sagdeev pseudopotential method was used to investigate the occurrence of stationary-profile solitary waves. We have determined how the electron-acoustic soliton characteristics depend on the electron beam parameters. It is found that the existence domain for solitons becomes narrower with an increase in the suprathermality of hot electrons, increasing the beam speed, decreasing the beam-to-cold electron population ratio. These results lead to a better understanding of the formation of electron-acoustic solitary waves observed in those space plasma systems characterized by kappa-distributed electrons and inertial drifting (beam) electrons.

Electron-acoustic solitons in an electron-beam plasma system with kappa-distributed electrons

We investigate the existence conditions and propagation properties of electron-acoustic solitary waves in a plasma consisting of an electron beam fluid, a cold electron fluid, and a hot suprathermal electron component modeled by a k-distribution function. The Sagdeev pseudopotential method was used to investigate the occurrence of stationary-profile solitary waves. We have determined how the soliton characteristics depend on the electron beam parameters. It is found that the existence domain for solitons becomes narrower with an increase in the suprathermality of hot electrons, increasing the beam speed, and decreasing the beam-to-cold electron population ratio.

The potential of electron beam irradiation for simultaneous surface modification and bioresorption control of PLLA for medical device applications

Bioresorbable polymers have been widely investigated as materials exhibiting significant potential for successful application in the medical fields of bone fixation devices and drug delivery. Further to the ability to control degradation, surface engineering of polymers has been highlighted as a key method central to their development. Previous work has demonstrated the ability of electron beam (e-beam) technology to control the degradation profiles and bioresorption of a number of commercially relevant bioresorbable polymers (poly-l-lactic acid (PLLA), L-lactide/ DL-lactide co-polymer (PLDL) and poly(lactic-co-glycolic acid) (PLGA). This work investigates the further potential of e-beam technology to impart added biofunctionality through the manipulation of polymer (PLLA) surface properties. A Dynamatron Continuous DC e-beam unit (Synergy Health, UK), with beam energies of 0.5, 0.75, and 1.5 MeV, was used for the irradiation of PLLA samples with delivered surface doses of 150 or 500 kGy at each energy level. The chosen conditions reflect the need to achieve a specific surface modification for the control of surface degradation as demonstrated in previous work. Surface characterization was then performed using contact angle analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy.
Results demonstrated a significant increase in surface wettability post e-beam treatment. In correlation with this, XPS data showed the introduction of oxygen-containing functional groups to the surface of PLLA. Raman spectroscopy indicated chain scission in the near surface region of PLLA. E-beam irradiation did not seem to affect the surface roughness of PLLA as a direct consequence of the treatment. In conclusion electron beam surface modification has been found to modify both the surface-to-bulk bioresorption profile and the surface hydrophilicity. Both could provide benefits in relation to the performance of implantable medical devices.

An efficient harmony search with new pitch adjustment for dynamic economic dispatch

A simple yet efficient harmony search (HS) method with a new pitch adjustment rule (NPAHS) is proposed for dynamic economic dispatch (DED) of electrical power systems, a large-scale non-linear real time optimization problem imposed by a number of complex constraints. The new pitch adjustment rule is based on the perturbation information and the mean value of the harmony memory, which is simple to implement and helps to enhance solution quality and convergence speed. A new constraint handling technique is also developed to effectively handle various constraints in the DED problem, and the violation of ramp rate limits between the first and last scheduling intervals that is often ignored by existing approaches for DED problems is effectively eliminated. To validate the effectiveness, the NPAHS is first tested on 10 popular benchmark functions with 100 dimensions, in comparison with four HS variants and five state-of-the-art evolutionary algorithms. Then, NPAHS is used to solve three 24-h DED systems with 5, 15 and 54 units, which consider the valve point effects, transmission loss, emission and prohibited operating zones. Simulation results on all these systems show the scalability and superiority of the proposed NPAHS on various large scale problems.

Experimental validation of a drive-by stiffness identification method for bridge monitoring

An experimental investigation is carried out to verify the feasibility of using an instrumented vehicle to detect and monitor bridge dynamic parameters. The low-cost method consists of the use of a moving vehicle fitted with accelerometers on its axles. In the laboratory experiment, the vehicle–bridge interaction model consists of a scaled two-axle vehicle model crossing a simply supported steel beam. The bridge model also includes a scaled road surface profile. The effects of varying the vehicle model configuration and speed are investigated. A finite element beam model is calibrated using the experimental results, and a novel algorithm for the identification of global bridge stiffness is validated. Using measured vehicle accelerations as input to the algorithm, the beam stiffness is identified with a reasonable degree of accuracy.

Entity Linking for Web Search Queries

We consider the problem of linking web search queries to entities from a knowledge base such as Wikipedia. Such linking enables converting a user’s web search session to a footprint in the knowledge base that could be used to enrich the user profile. Traditional methods for entity linking have been directed towards finding entity mentions in text documents such as news reports, each of which are possibly linked to multiple entities enabling the usage of measures like entity set coherence. Since web search queries are very small text fragments, such criteria that rely on existence of a multitude of mentions do not work too well on them. We propose a three-phase method for linking web search queries to wikipedia entities. The first phase does IR-style scoring of entities against the search query to narrow down to a subset of entities that are expanded using hyperlink information in the second phase to a larger set. Lastly, we use a graph traversal approach to identify the top entities to link the query to. Through an empirical evaluation on real-world web search queries, we illustrate that our methods significantly enhance the linking accuracy over state-of-the-art methods.

Electron-impact ionization of argon using the R-matrix with a pseudo-states method

Electron-impact ionization cross sections for argon are calculated using both non-perturbative R-matrix with pseudo-states (RMPS) and perturbative distorted-wave methods. At twice the ionization potential, the 3p(61)S ground-term cross section from a distorted-wave calculation is found to be a factor of 4 above crossed-beams experimental measurements, while with the inclusion of term-dependent continuum effects in the distorted-wave method, the perturbative cross section still remains almost a factor of 2 above experiment. In the case of ionization from the metastable 3p(5)4s(3)P term, the distorted-wave ionization cross section is also higher than the experimental cross section. On the other hand, the ground-term cross section determined from a nonperturbative RMPS calculation that includes 27 LS spectroscopic terms and another 282 LS pseudo-state terms to represent the high Rydberg states, and the target continuum is found to be in excellent agreement with experimental measurements, while the RMPS result is below the experimental cross section for ionization from the metastable term. We conclude that both continuum term dependence and interchannel coupling effects, which are included in the RMPS method, are important for ionization from the ground term, and interchannel coupling is also significant for ionization from the metastable term

Nanostructuring Ferroelectrics via Focused Ion Beam Methodologies

As we reach the physical limit of Moore’s law and silicon based electronics, alternative schemes for memory and sensor devices are being proposed on
a regular basis. The properties of ferroelectric materials on the nanoscale are key to developing device applications of this intriguing material class, and nanostructuring has been readily pursued in recent times. Focused ion beam (FIB) microscopy is one of the most signi cant techniques for achieving
this. When applied in tandem with the imaging and nanoscale manipulation afforded by proximal scanning force microscopy tools, FIB-driven nanoscale characterization has demonstrated the power and ability which simply may not be possible by other fabrication techniques in the search for innovative and novel ferroic phenomena. At the same time the process is not without pitfalls; it is time-consuming and success is not always guaranteed thus often being the bane in progress. This balanced review explores a brief history of the relationship between the FIB and ferroelectrics, the fascinating properties it has unveiled, the challenges associated with FIB that have led to alterna- tive nanostructuring techniques and nally new ideas that should be explored using this exciting technique.