Simulations of electric field domain suppression in a superlattice oscillator device using a distributed circuit model

We present a method for simulating static domain formation in distributed negative differential resistance devices using a distributed circuit array model coupled with quantum transport simulations. This simulation method is applied to the case of a superlattice Bloch oscillator to ascertain the efficacy of electric field domain wall suppression by micro shunt side walls. Two independent simulation mechanisms using the same basic distributed circuit model are employed to separate simulation artifacts from true physical trends. Simulations are presented, suggesting that the presence of the micro shunt can suppress domain formation above a critical device bias voltage. The simulated dependence of this critical voltage on macroscopic device parameters is presented.     

Noncentrosymmetric Tetrel Pnictides RuSi4P4 and IrSi3P3: Nonlinear Optical Materials with Outstanding Laser Damage Threshold

Noncentrosymmetric (NCS) tetrel pnictides have recently generated interest as nonlinear optical (NLO) materials due to their second harmonic generation (SHG) activity and large laser damage threshold (LDT). Herein nonmetal-rich silicon phosphides RuSi₄P₄ and IrSi₃P₃ are synthesized and characterized. Their crystal structures are reinvestigated using single crystal X-ray diffraction and ²⁹Si and ³¹P magic angle spinning NMR. In agreement with previous report RuSi₄P₄ crystallizes in NCS space group P1, while IrSi₃P₃ is found to crystallize in NCS space group Cm, in contrast with the previously reported space group C2. A combination of DFT calculations and diffuse reflectance measurements reveals RuSi₄P₄ and IrSi₃P₃ to be wide bandgap (E_g) semiconductors, E_g = 1.9 and 1.8 eV, respectively. RuSi₄P₄ and IrSi₃P₃ outperform the current state-of-the-art infrared SHG material, AgGaS₂, both in SHG activity and laser inducer damage threshold. Due to the combination of high thermal stabilities (up to 1373 K), wide bandgaps (≈2 eV), NCS crystal structures, strong SHG responses, and large LDT values, RuSi₄P₄ and IrSi₃P₃ are promising candidates for longer wavelength NLO materials.     

Active contour external force using vector field convolution for image segmentation.

Snakes, or active contours, have been widely used in image processing applications. Typical roadblocks to consistent performance include limited capture range, noise sensitivity, and poor convergence to concavities. This paper proposes a new external force for active contours, called vector field convolution (VFC), to address these problems. VFC is calculated by convolving the edge map generated from the image with the user-defined vector field kernel. We propose two structures for the magnitude function of the vector field kernel, and we provide an analytical method to estimate the parameter of the magnitude function. Mixed VFC is introduced to alleviate the possible leakage problem caused by choosing inappropriate parameters. We also demonstrate that the standard external force and the gradient vector flow (GVF) external force are special cases of VFC in certain scenarios. Examples and comparisons with GVF are presented in this paper to show the advantages of this innovation, including superior noise robustness, reduced computational cost, and the flexibility of tailoring the force field.     

MobileNAT: A New Technique for Mobility Across Heterogeneous Address Spaces

We propose a new network layer mobility architecture called Mobile NAT to efficiently support micro and macro-mobility in and across heterogeneous address spaces common in emerging public networks. The key ideas in this architecture are as follows: (1) Use of two IP addresses – an invariant virtual IP address for host identification at the application layer and an actual routable address at the network layer that changes due to mobility. Since physical address has routing significance only within a domain, it can be a private address and therefore, does not deplete the public IP address resource. (2) New DHCP enhancements to distribute the two addresses. (3) A new signaling element called Mobility Manager (MM) that uses Middlebox Communication (MIDCOM) framework to signal the changes in packet processing rules to the Network Address Translators (NATs) in the event of node mobility. Our proposal does not require any modifications to the access networks and can seamlessly co-exist with the existing Mobile IP mechanisms and therefore, can be used to provide seamless mobility across heterogeneous wireline and wireless networks. We report implementation details of a subset of our ideas in a testbed with Windows XP clients and Linux based NATs. Milind M. Buddhikot is a Member of Technical Staff in the Center for Networking Research at Lucent Bell Labs, Holmdel, NJ. Milind holds a Doctor of Science (D. Sc.) in computer science (July 1998) from Washington University in St. Louis, and a Master of Technology (M.Tech.) in communication engineering (December 1988) from the Indian Institute of Technology (I.I.T), Bombay. His current research interests are in the areas of systems and protocols for integrated public wireless networks, authentication and dynamic key exchange protocols, Voice-over-IP (VOIP) networks, and sensor and ad-hoc networks. He has authored over 26 research papers and 9 patent submissions in the areas of design of multimedia systems and protocols, layer-4 packet classification, MPLS path routing, authentication and dynamic key exchange, and 802.11/3G integration. Milind currently serves as the Associate Editor of the IEEE/ACM Transactions on Networking. He also served as a co-guest-editor of IEEE Network magazine’s March 2001 Special issue on Fast IP Packet forwarding and Classification for Next Generation Internet Services. He has served in the capacity of a tutorial chair for IEEE LCN 94, 95, as a publicity chair for NOSSDAV97, and as a program committee member for MMCN 2001, 2003, IEEE ICNP2002, 2003 and IEEE LCN 93-2000 conferences. Adiseshu Hari received a Doctorate in Computer Science from Washington University in St. Louis in 1999, and has since been at Bell Labs, Lucent Technologies, where he’s worked on projects related to network design and optimization. He’s currently looking at design issues in large scale SIP based VoIP networks. Kundan N. Singh received a B.E.(Hons) degree in Computer Science from Birla Institute of Technology and Science in India, M.S. in Computer Science from Columbia University, and is continuing his studies towards Ph.D. degree in the same field at Columbia University in New York City. As a research assistant in the Internet Real-Time Lab at Columbia University, he is doing research on Internet telephony, SIP-H.323 signaling gateway, unified messaging systems and multimedia conferencing. Scott Miller is the Director of the High Speed Mobile Data Research department at Bell Labs in Holmdel, New Jersey. He has B.S. and M.S. degrees in electrical engineering from Cooper Union in New York City. His current research involves the integration of 802.11 and 3G wireless data service and the related mobile networking issues concerning seamless mobility, authentication, security, roaming, and accounting. Prior to his work on 802.11/3G integration, Scott has led several systems research efforts in wireless applications, implementing novel systems for wireless messaging, speech-driven directory services, wireless instant messaging, carrier-based content billing, and multi-media content adaptation.This revised version was published online in August 2005 with a corrected cover date.     

Ten-inch molecular beam epitaxy production system for HgCdTe growth

Growth of Hg_1−xCd_xTe by molecular beam epitaxy (MBE) has been under development since the early 1980s at Rockwell Scientific Company (RSC), formerly the Rockwell Science Center; and we have shown that high-performance and highly reproducible MBE HgCdTe double heterostructure planar p-on-n devices can be produced with high throughput for various single- and multiplecolor infrared applications. In this paper, we present data on Hg_1−xCd_xTe epitaxial layers grown in a ten-inch production MBE system. For growth of HgCdTe, standard effusion cells containing CdTe and Te were used, in addition to a Hg source. The system is equipped with reflection high energy electron diffraction (RHEED) and spectral ellipsometry in addition to other fully automated electrical and optical monitoring systems. The HgCdTe heterostructures grown in our large ten-inch Riber 49 MBE system have outstanding structural characteristics with etch-pit densities (EPDs) in the low 10⁴ cm⁻² range, Hall carrier concentration in low 10¹⁴ cm⁻³, and void density <1000 cm². The epilayers were grown on near lattice-matched (211)B Cd_0.96Zn_0.04Te substrates. High-performance mid wavelength infrared (MWIR) devices were fabricated with R₀A values of 7.2×10⁶ Ω-cm² at 110 K, and the quantum efficiency without an antireflection coating was 71.5% for cutoff wavelength of 5.21 μm at 37 K. For short wavelength infrared (SWIR) devices, an R₀A value of 9.4×10⁵ Ω-cm² at 200 K was obtained and quantum efficiency without an antireflection coating was 64% for cutoff wavelength of 2.61 μm at 37 K. These R₀A values are comparable to our trend line values in this temperature range.     

Organic Materials and Thin‐Film Structures for Cross‐Point Memory Cells Based on Trapping in Metallic Nanoparticles

Non‐volatile solid‐state memory cells based on composites of metal nanoparticles and polymers are embedded in organic semiconducting host materials. This paper presents data from a wide range of materials and device structures and shows that the switching phenomenon is commonly observed.     

A low-jitter 125-1250-MHz process-independent and ripple-poleless0.18-μm CMOS PLL based on a sample-reset loop filter

This paper describes a low-jitter phase-locked loop (PLL) implemented in a 0.18-μm CMOS process. A sample-reset loop filter architecture is used that averages the oscillator proportional control current which provides the feedforward zero over an entire update period and hence leads to a ripple-free control signal. The ripple-free control current eliminates the need for an additional filtering pole, leading to a nearly 90° phase margin which minimizes input jitter peaking and transient locking overshoot. The PLL damping factor is made insensitive to process variations by making it dependent only upon a bandgap voltage and ratios of circuit elements. This ensures tracking between the natural frequency and the stabilizing zero. The PLL has a frequency range of 125-1250 MHz, frequency resolution better than 500 kHz, and rms jitter less than 0.9% of the oscillator period     

Macrophage Immunomodulation Through New Polymers that Recapitulate Functional Effects of Itaconate as a Power House of Innate Immunity

Itaconate (ITA) is an emerging powerhouse of innate immunity with therapeutic potential that is limited in its ability to be administered in a soluble form. A library of polyester materials that incorporate ITA into polymer backbones resulting in materials with inherent immunoregulatory behavior is developed. Harnessing hydrolytic degradation release from polyester backbones, ITA polymers result in the mechanism specific immunoregulatory properties on macrophage polarization in vitro. In a functional assay, the polymer-released ITA inhibits bacterial growth on acetate. Translation to an in vivo model of biomaterial associated inflammation, intraperitoneal injection of ITA polymers demonstrate a rapid resolution of inflammation in comparison to a control polymer silicone, demonstrating the value of sustained biomimetic presentation of ITA.     

The use of network delay estimation for multimedia data retrieval

Multimedia data have specific temporal presentation requirements. For example in video conferencing applications the voice and images of the participants must be delivered and presented synchronously. These requirements can be achieved by scheduling or managing system resources. We present a technique called limited a priori scheduling (LAP) to manage the delivery channel from source to destination for digital multimedia data. By using delay estimation a LAP scheduler can retrieve stored digital media spanning arbitrary networks with unspecified delays. The use of delay estimation also facilitates selective degradation of service in bandwidth and buffer limited situations. Such degradation enables the continuous real-time playout and synchronization of various media arriving from different sources. The performance of the LAP scheduler is described based on implementation and experimentation using Ethernet     

Correlation of electron and proton-irradiation-induced damage in InP solar cells

The measured degradation of epitaxial shallow homojunction n⁺p InP solar cells under 1-MeV electron irradiation is correlated with that measured under 3-MeV proton irradiation based on ‘displacement damage dose’. The measured data are analyzed as a function of displacement damage dose from which an electron-to-proton dose equivalency ratio is determined which enables the electron and proton degradation data to be described by a single degradation curve. It is discussed how this single curve can be used to predict the cell degradation under irradiation by any particle energy. The degradation curve is used to compare the radiation response of InP and GaAs/Ge cells on an absolute damage energy scale. The comparison shows InP to be inherently more resistant to displacement damage deposition than the GaAs/Ge.