Mechanical Properties of Robust Ultrathin Silk Fibroin Films

Robust ultrathin multilayer films of silk fibroin were fabricated by spin coating and spin‐assisted layer‐by‐layer assembly and their mechanical properties were studied both in tensile and compression modes for the first time. The ultrathin films were characterized by a high elastic modulus of 6–8 GPa (after treatment with methanol) with the ultimate tensile strength reaching 100 MPa. The superior toughness is also many times higher than that usually observed for conventional polymer composites (328 kJ m^–3 for the silk material studied here versus typical values of < 100 kJ m^–3). These outstanding properties are suggested to be caused by the gradual development of the self‐reinforcing microstructure of highly crystalline β‐sheets, serving as reinforcing fillers and physical crosslinks, a process that is well known for bulk silk materials but it is demonstrated here to occur in ultrathin films as well, despite their limited dimensions. However, the confined state within films thinner than the lengths of the extended domains causes a significantly reduced elasticity which should be considered in the design of nanosized films from silk materials. Such regenerated silk fibroin films with outstanding mechanical strength have potential applications in microscale biodevices, biocompatible implants, and synthetic coatings for artificial skin.     

A networked mobile sensor test-bed for collaborative multi-target tracking applications

This paper presents the design, architecture, implementation, and experimental results from a networked mobile sensor test-bed developed for collaborative sensor tracking applications. The test-bed comprises a fleet of networked mobile sensors, an indoor localization system, a control, debugging and management infrastructure, and a tiered wireless ad hoc network for seamless integration of the above three components and the existing wireless infrastructure. First, the software and hardware architectural details of a swarm capable autonomous vehicle (SCAV) system for our collaborative applications are presented. Second, the details of an indoor self-localization and Kalman filter based navigation system design for the SCAV platform are presented. Third, as an example multi-sensor application, a collaborative multi-target tracking problem and a heuristics-based networked solution are formulated. Finally, the performance of the collaborative tracking framework is evaluated on the laboratory test-bed for characterizing the impacts of localization and navigation errors on the distributed tracking performance. The experimental study also characterizes the tradeoff between the tracking performance and the consumed wireless bandwidth. The experimental results demonstrate a number of counterintuitive results due to various errors in sensor localization and navigation.     

Photo-assisted metal-organic chemical vapor deposition of CaCu3Ti4O12 (CCTO) thin films

Calcium copper titanate (CaCu₃Ti₄O₁₂) or CCTO is one of the most researched giant dielectric constant materials in recent years. In the present work, incoherent light source based photo-assisted metal-organic chemical vapor deposition (MOCVD) has been used to prepare CCTO thin films on Si/SiO₂ substrates. Key to this unique processing technique is the use of UV radiation as an additional source of energy in conjunction to the thermal energy. The given Photo-assisted MOCVD processing resulted in polycrystalline CCTO growth on a SiO₂ surface. Powder X-ray diffraction and scanning electron microscopy were performed to analyze structural and compositional properties of the CCTO thin film. Ellipsometric measurements indicated a refractive index of 3.03 for the CCTO thin film.     

Minimum selection GSC in independent Rayleigh fading

We analyze the error performance of minimum selection generalized selection combining (MS-GSC), in which the minimum number of diversity branches are selected such that their combined signal-to-noise ratio (SNR) is above a given threshold. A flat Rayleigh fading channel with independent and distinctly distributed branch SNRs is considered. By transforming the ordered instantaneous branch SNRs to their differences, we derive the distribution of the number of selected branches in closed form. We then modify the derivation of this distribution to get the characteristic function (cf.) of the combiner output SNR. This cf. is used to obtain the symbol error probability for different coherent digital modulation schemes.     

Hybrid mode-switched control of DC-DC boost converter circuits

This paper has proposed a new switching scheme for controlling dc-dc boost converter circuits. The converter is represented as a hybrid system with three modes of operation. The switching among these modes is governed by the adjustable reference voltage and a reference current which are calculated by an energy balance principle. The scheme has been applied to a realistic converter circuit modeled with various parasitic components. All the specifications related to the ripple voltage, line and load regulation are shown to be achievable by relating them to the switching surfaces, namely a reference voltage and a reference current. The state trajectories have been shown to reach a hybrid limit cycle already proved to be super-stable from consideration of chaos. Numerical results clearly bring out the advantages of the proposed control scheme.     

Scattering of a Monopolar TE-Polarized Electromagnetic Pulse on an Ideally Conducting Cylinder

Journal of Communications Technology and Electronics - Abstract—The problem of scattering on an ideally conducting infinite cylinder of a monopolar electromagnetic pulse, the electric field...     

Maximizing Parallel Testing in an FM Receiver

High volume production environments create great challenges for production testing and verification of Radio Frequency (RF) devices. In this environment, much emphasis is put on parallel testing, or the ability to test multiple devices at the same time using a single tester. In order for this parallelism to become a reality, there is a need for production RF tests to be simplified and reduced to requiring only the simplest test stimulus and analysis. In this paper, we present a new method of measuring the performance of a Frequency Modulation (FM) receiver that requires only a continuous wave signal input in order to eliminate the more costly Signal-to-Noise Ratio test. Using this new technique we will then demonstrate how simplifying this test and adding frequency diversity enables testing of up to 8 devices in parallel using a single tester.     

Anisotropy of Charge Transport in a Uniaxially Aligned and Chain‐Extended,High‐Mobility,Conjugated Polymer Semiconductor

Charge transport in the ribbon phase of poly(2,5‐bis(3‐alkylthiophen‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT)—one of the most highly ordered, chain‐extended crystalline microstructures available in a conjugated polymer semiconductor—is studied. Ribbon‐phase PBTTT has previously been found not to exhibit high carrier mobilities, but it is shown here that field‐effect mobilities depend strongly on the device architecture and active interface. When devices are constructed such that the ribbon‐phase films are in contact with either a polymer gate dielectric or an SiO₂ gate dielectric modified by a hydrophobic, self‐assembled monolayer, high mobilities of up to 0.4 cm² V^?1 s^?1 can be achieved, which is comparable to those observed previously in terrace‐phase PBTTT. In uniaxially aligned, zone‐cast films of ribbon‐phase PBTTT the mobility anisotropy is measured for transport both parallel and perpendicular to the polymer chain direction. The mobility anisotropy is relatively small, with the mobility along the polymer chain direction being higher by a factor of 3–5, consistent with the grain size encountered in the two transport directions.     

Principles and demonstration of multi-functional adaptive electromagnetic screen

A bidirectional electromagnetic screen is proposed and demonstrated with properties that can be switched between high reflection, absorption and transmission over /spl sim/10 ns. The screen comprises frequency selective surfaces loaded with pin diodes, which under partial biasing conditions provide the loss mechanism for the absorption state of the screen.