Low frequency noise spectroscopy in InAs/GaAs resonant tunneling quantum dot infrared photodetectors

We have studied the temperature dependence of low-frequency noise in InAs–GaAs resonant tunneling quantum dot infrared photodetectors (T-QDIPs). The noise in these devices has been investigated in the temperature range of 78–300 K. The noise spectrum showed a weak Lorentzian component superimposed upon the 1/f^γ spectrum. The change in the cut-off frequency of the Lorentzian was analyzed as a function of temperature. The activation energy of the trap associated with this Lorentzian was obtained as 0.155 eV, which is in good agreement with the energy of the lowest energy state in the quantum dot.     

Direct‐Write Assembly of Microperiodic Silk Fibroin Scaffolds for Tissue Engineering Applications

Three–dimensional, microperiodic scaffolds of regenerated silk fibroin have been fabricated for tissue engineering by direct ink writing. The ink, which consisted of silk fibroin solution from the Bombyx mori silkworm, was deposited in a layer‐by‐layer fashion through a fine nozzle to produce a 3D array of silk fibers of diameter 5 µm. The extruded fibers crystallized when deposited into a methanol‐rich reservoir, retaining a pore structure necessary for media transport. The rheological properties of the silk fibroin solutions were investigated and the crystallized silk fibers were characterized for structure and mechanical properties by infrared spectroscopy and nanoindentation, respectively. The scaffolds supported human bone marrow‐derived mesenchymal stem cell (hMSC) adhesion, and growth. Cells cultured under chondrogenic conditions on these scaffolds supported enhanced chondrogenic differentiation based on increased glucosaminoglycan production compared to standard pellet culture. Our results suggest that 3D silk fibroin scaffolds may find potential application as tissue engineering constructs due to the precise control of their scaffold architecture and their biocompatibility.     

HotSpot: a compact thermal modeling methodology for early-stage VLSI design

This paper presents HotSpot-a modeling methodology for developing compact thermal models based on the popular stacked-layer packaging scheme in modern very large-scale integration systems. In addition to modeling silicon and packaging layers, HotSpot includes a high-level on-chip interconnect self-heating power and thermal model such that the thermal impacts on interconnects can also be considered during early design stages. The HotSpot compact thermal modeling approach is especially well suited for preregister transfer level (RTL) and presynthesis thermal analysis and is able to provide detailed static and transient temperature information across the die and the package, as it is also computationally efficient.     

Kitkaite NiTeSe,an Ambient-Stable Layered Dirac Semimetal with Low-Energy Type-II Fermions with Application Capabilities in Spintronics and Optoelectronics

The emergence of Dirac semimetals has stimulated growing attention, owing to the considerable technological potential arising from their peculiar exotic quantum transport related to their nontrivial topological states. Especially, materials showing type-II Dirac fermions afford novel device functionalities enabled by anisotropic optical and magnetotransport properties. Nevertheless, real technological implementation has remained elusive so far. Definitely, in most Dirac semimetals, the Dirac point lies deep below the Fermi level, limiting technological exploitation. Here, it is shown that kitkaite (NiTeSe) represents an ideal platform for type-II Dirac fermiology based on spin-resolved angle-resolved photoemission spectroscopy and density functional theory. Precisely, the existence of type-II bulk Dirac fermions is discovered in NiTeSe around the Fermi level and the presence of topological surface states with strong (≈50%) spin polarization. By means of surface-science experiments in near-ambient pressure conditions, chemical inertness towards ambient gases (oxygen and water) is also demonstrated. Correspondingly, NiTeSe-based devices without encapsulation afford long-term efficiency, as demonstrated by the direct implementation of a NiTeSe-based microwave receiver with a room-temperature photocurrent of 2.8 µA at 28 GHz and more than two orders of magnitude linear dynamic range. The findings are essential to bringing to fruition type-II Dirac fermions in photonics, spintronics, and optoelectronics.     

Optimal Location of Energy Efficient DF Relay Node in $$\varvec{\kappa}$$ κ – $$\varvec{\mu }$$ μ Fading Channel

We investigate the optimal location of an adaptive decode and forward relay operating over a \(\kappa\)–\(\mu\) fading channel. The \(\kappa\)–\(\mu\) statistics provides a generalized line-of-sight propagation model which includes fading models like Rayleigh, Nakagami, Rician as special cases. We restrict our analysis to collinear relay placement, i.e. the relay node \((R_n)\) is on the same straight line between the source node \((S_n)\) and the destination node \((D_n)\). In the non-cooperative mode, \(D_n\) accepts only the two-hop transmission via \(R_n\) and discards any direct signal that may be available from \(S_n\). On the other hand, in the cooperative mode, \(D_n\) accepts both the replicas and combine them following either selection combining (SC) or maximum ratio combining (MRC). It is interesting to see that such cooperation does not always lead to energy saving, especially for small \(S_n-D_n\) separation. Also, worth mentioning the fact that MRC may not be optimal from the energy efficiency perspective, and SC can outperform MRC under certain channel conditions. In our paper, we also studied how parameters like spectral efficiency (R), path loss exponent (n), and fading parameters (\(\kappa ,\mu\)) affect the optimal relay placement location.

     

An electronically tunable microstrip bandpass filter using thin-film Barium-Strontium-Titanate (BST) varactors

A tunable third-order combline bandpass filter using thin-film barium-strontium-titanate varactors and fabricated on a sapphire substrate is reported. Application of 0-200-V bias varied the center frequency of the filter from 2.44 to 2.88 GHz (16% tuning) while achieving a 1-dB bandwidth of 400 MHz. The insertion loss varied from 5.1 dB at zero bias to 3.3 dB at full bias, while the return loss exceeded 13 dB over the range. The third-order intercept of the filter was found to be 41 dBm.     

Structural,electrical and optical properties of sintered SnO2 pellets

Tin dioxide (SnO₂) powder was prepared by the co-precipitation method using SnCl₂ solution as a precursor. The powder was then pelletized and sintered. Structural characterization of the samples with XRD confirmed that all the pellets were of SnO₂ having polycrystalline nature with the crystallite size of the order of 90 nm. SEM-EDAX was used to confirm the morphology and composition of the samples. The measurements of electrical properties were carried out in the frequency range of 100 Hz to 100 kHz at various fixed temperatures from 40 °C to 160 °C. The a.c. conductivity and the dielectric constant were found to be dependent on both frequency and temperature. The frequency and temperature dependent conduction properties of SnO₂ are found to be in accordance with correlated barrier hoping model. Infrared and visible spectroscopic studies show that a strong vibration band characteristic of the SnO₂ stretching mode was present at around 620 cm^?1 and the samples exhibited optical transmittance in the visible range.     

A game theory-based approach for the study of inter-interference in coexisting wireless body area networks

A wireless body area network (WBAN) enables the continuous monitoring of health conditions including heart rate, temperature, and glucose levels. It is composed of several sensors that are placed on the body. The network's performance is significantly affected by the unpredictable movements of the human body. Due to the varying proximities between them, the existence of several WBANs creates a challenge when mobility is involved. In this fictitious scenario, we consider a park area with both mobile and static WBANs or WBAN-equipped individuals passing through the park who have varying degrees of mobility. When a mobile WBAN passes a static WBAN and is within a minimum distance of the static WBAN, they pair up and immediately interfere. Inter-interference caused by WBANs operating in a limited area causes packet loss and performance deterioration. In this work, static WBAN locations are optimised to minimise interference and system inter-interference problems are addressed by a game theoretic method. This paper formulates a flexible game theoretic framework to study WBAN coexistence using the expected pay-off function considering a two-player game. It is observed from the results obtained that the probability of interference caused by fast mobile WBANs is reduced to a maximum of 50% compared with that caused by slow mobile WBANs thereby reducing the need for relocation of static WBANs.     

Low-power scan design using first-level supply gating

Reduction in test power is important to improve battery lifetime in portable electronic devices employing periodic self-test, to increase reliability of testing, and to reduce test cost. In scan-based testing, a significant fraction of total test power is dissipated in the combinational block. In this paper, we present a novel circuit technique to virtually eliminate test power dissipation in combinational logic by masking signal transitions at the logic inputs during scan shifting. We implement the masking effect by inserting an extra supply gating transistor in the supply to ground path for the first-level gates at the outputs of the scan flip-flops. The supply gating transistor is turned off in the scan-in mode, essentially gating the supply. Adding an extra transistor in only one logic level renders significant advantages with respect to area, delay, and power overhead compared to existing methods, which use gating logic at the output of scan flip-flops. Moreover, the proposed gating technique allows a reduction in leakage power by input vector control during scan shifting. Simulation results on ISCAS89 benchmarks show an average improvement of 62% in area overhead, 101% in power overhead (in normal mode), and 94% in delay overhead, compared to the lowest cost existing method.     

An architecture for next-generation radio access networks

With fourth-generation wireless technologies envisioned to provide high bandwidth for content-rich multimedia applications, next-generation mobile communication systems are well poised to lead the technology march. Incumbent with the new technology is the challenge of providing flexible, reconfigurable architectures capable of catering to the dynamics of the network, while providing cost-effective solutions for service providers. In this article we focus on IP-based radio access network architectures for next-generation mobile systems. We provide an insight into wireless mesh-based connectivity for the RAN network elements - using short high-bandwidth links to interconnect the network entities in a multihop mesh network for backhauling traffic to the core. A generic self-similar fractal topology, using optical wireless transmission technology, is described. We study the performance of the architecture and conclude that mesh-based architectures are well suited to provide highly scalable, dynamic radio access networks with carrier-class features at significantly low system costs.