A model for rational abandonments from invisible queues

We propose a model for abandonments from a queue, due to excessive wait, assuming that waiting customers act rationally but without being able to observe the queue length. Customers are allowed to be heterogeneous in their preferences and consequent behavior. Our goal is to characterize customers' patience via more basic primitives, specifically waiting costs and service benefits: these two are optimally balanced by waiting customers, based on their individual cost parameters and anticipated waiting time. The waiting time distribution and patience profile then emerge as an equilibrium point of the system. The problem formulation is motivated by teleservices, prevalently telephone- and Internet-based. In such services, customers and servers are remote and queues are typically associated with the servers, hence queues are invisible to waiting customers. Our base model is the M/M/m queue, where it is shown that a unique equilibrium exists, in which rational abandonments can occur only upon arrival (zero or infinite patience for each customer). As such a behavior fails to capture the essence of abandonments, the base model is modified to account for unusual congestion or failure conditions. This indeed facilitates abandonments in finite time, leading to a nontrivial, customer dependent patience profile. Our analysis shows, quite surprisingly, that the equilibrium is unique in this case as well, and amenable to explicit calculation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Intraosseous monitoring and guiding by ultrasound: A feasibility study

An efficient method for navigation within bone tissue boundaries is essential for performance of surgical procedures, e.g. without damaging of adjacent vulnerable organs. The application of sonographic measuring methods for this purpose promises to be effective in the ability to distinguish soft trabecular bone from dense cortical bone, owing to an order of magnitude difference in acoustic density between these structures. For this purpose, a specific method was developed that utilizes propagation of a 5 MHz ultrasonic wave through an aqueous milieu. Using this method a 0.2 mm resolution in measurements is achieved. This resolution is in an order of magnitude lower than is required for a clinical use. A three-stage experimental approach was adopted: measurements in a cubic “phantom” made of a transparent plastic material, in samples of fresh porcine femora, and in a clinical setting of drilling in the upper and lower jaw during dental implantation surgery in nine patients. Two patterns of the detected ultrasound wave reflections were found: low amplitude reflections from the aqueous surrounding and trabecular bone and highly reflected ultrasound waves from the cortical bone. We show that trabecular and cortical bones are distinguishable by real-time ultrasonic measurement. The distances of the drilled tracts, in the range of 58.0–122.0 mm for the “phantom” experiment, 22.6–35.5 mm for the ex vivo experiment and 10.0–11.5 mm in the clinical experiment, and residual distances to the opposite edge of the tested samples and organs, in the range of 21.0–82.0 mm for the “phantom” experiment, 3.8–11.36 mm for the ex vivo experiment and 2.1–6.9 mm in the clinical experiment, were measured by the presented sonographic method and compared statistically, using linear correlation and Bland Altman plot, to the mechanical and/or radiographic measurements in all three stages of the experiment. A correlation coefficient above 0.95 was considered an indication of high correlation, while a value of 0.75–0.94 was considered intermediate, and a value below 0.75 was considered poor.     

Durable bonding of silica nanoparticles to polymers by photoradiation for control of surface properties

Improvement of superhydrophobic surfaces durability is a critical key for potential commercial applications such as self‐cleaning and ice repellency. In this study, functionalization of silica nanoparticles by photoreactive benzophenone groups was made in order to covalently bond nanoparticles to polymer substrates to obtain durable coatings. Upon ultraviolet irradiation reactive excited triplet benzophenone species are formed enabling them to react with the polymer matrix through hydrogen abstraction. Two matrices were studied: radiation‐curable urethane acrylate and epoxy. The bonding of the particles to the surfaces was evaluated using atomic force microscope nanomanipulation and cross‐section analysis. The results have shown a greater stability of the photoreactive silica nanoparticles. Copyright © 2014 John Wiley & Sons, Ltd.     

Biomolecular detection with a thin membrane transducer

We present a thin membrane transducer (TMT) that can detect nucleic acid based biomolecular reactions including DNA hybridization and protein recognition by aptamers. Specific molecular interactions on an extremely thin and flexible membrane surface cause the deflection of the membrane due to surface stress change which can be measured by a compact capacitive circuit. A gold-coated thin PDMS membrane assembled with metal patterned glass substrate is used to realize the capacitive detection. It is demonstrated that perfect match and mismatch hybridizations can be sharply discriminated with a 16-mer DNA oligonucleotide immobilized on the gold-coated surface. While the mismatched sample caused little capacitance change, the perfectly matched sample caused a well-defined capacitance decrease vs. time due to an upward deformation of the membrane by a compressive surface stress. Additionally, the TMT demonstrated the single nucleotide polymorphism (SNP) capabilities which enabled a detection of mismatching base pairs in the middle of the sequence. It is intriguing that the increase of capacitance, therefore a downward deflection due to tensile stress, was observed with the internal double mismatch hybridization. We further present the detection of thrombin protein through ligand-receptor type recognition with 15-mer thrombin aptamer as a receptor. Key aspects of this detection such as the effect of concentration variation are investigated. This capacitive thin membrane transducer presents a completely new approach for detecting biomolecular reactions with high sensitivity and specificity without molecular labelling and optical measurement.     

A quantum mechanics/molecular mechanics study of the protein-ligand interaction of two potent inhibitors of human O-GlcNAcase: PUGNAc and NAG-thiazoline

O-glycoprotein 2-acetamino-2-deoxy-beta- d-glucopyranosidase ( O-GlcNAcase) hydrolyzes 2-acetamido-2-deoxy-beta- d-glucopyranose ( O-GlcNAc) residues of serine/threonine residues of modified proteins. O-GlcNAc is present in many intracellular proteins and appears to have a role in the etiology of several diseases including cancer, Alzheimer's disease, and type II diabetes. In this work, we have carried out molecular dynamics simulations using a hybrid quantum mechanics/molecular mechanics approach to determine the binding of two potent inhibitors, PUGNAc and NAG, with a bacterial O-GlcNAcase. The results of these simulations show that Asp-401, Asp-298, and Asp-297 residues play an important role in the protein-inhibitor interactions. These results might be useful to design compounds with more interesting inhibitory activity on the basis of its three-dimensional structure.     

Stimulated Brillouin scattering in highly birefringent microstructure fiber: experimental analysis

We report on an experimental analysis of stimulated Brillouin scattering (SBS) in a 20-m-long highly birefringent microstructure fiber for sensing applications. In particular, an experimental setup based on Brillouin optical frequency-domain analysis, operating at a wavelength of 1550 nm, has been employed in order to analyze the distribution of Brillouin frequency shift along the fiber, as well as to study the dependence of Brillouin frequency shift on optical polarization, temperature, and strain. Our results indicate that, for any fixed polarization, the fiber has a dual-peaked Brillouin spectrum. A study about the origin of these two peaks is presented.     

Cathodoluminescence and isochronal annealing investigations of edge-emission in ZnTe

Investigation of the liquid helium temperature cathodoluminescence edge-emission of undoped ZnTe has shown that two bands at 545.8 and 547.3 nm result respectively from free-to-bound and donor-acceptor pair recombination at a common acceptor level with a hole binding energy of 124 meV. From observations of the changes that occur in the edge-emission spectrum after isochronal (30 min) annealing treatments in vacuum in the temperature range 50–500°C it is suggested either that the acceptor defect is mobile and can move out of sites at which it behaves as an acceptor to sites at which it behaves as a donor or, during annealing complexing occurs which changes the nature of the centre and effectively removes it.     

On the asymptotic optimality of the <Emphasis Type="Italic">cμ</Emphasis>/<Emphasis Type="Italic">θ</Emphasis> rule under ergodic cost

We consider an overloaded multi-server multi-class queueing model where customers may abandon while waiting to be served. For class i, service is provided at rate μ _i , and abandonment occurs at rate θ _i . In a many-server fluid regime, we show that prioritizing the classes in decreasing order of c _i μ _i /θ _i asymptotically minimizes an ergodic holding cost, where c _i denotes the equivalent holding cost per unit time for class i.     

An Explicit Factorization Algorithm

In this paper a new algorithm is proposed for explicit factorization of 2 x 2 matrix functions.