Electrostatic actuators exhibit fast response times and are easily integrated into microsystems because they can be fabricated with standard IC micromachining processes and materials. Although electrostatic actuators have been used extensively in 'dry' MEMS, they have received less attention in microfluidic systems probably because of challenges such as electrolysis, anodization, and electrode polarization. Here we demonstrate that ac drive signals can be used to prevent electrode polarization, and thus enable electrostatic actuation in many liquids, at potentials low enough to avoid electrochemistry. We measure the frequency response of an interdigitated silicon comb-drive actuator in liquids spanning a decade of dielectric permittivities and four decades of conductivity, and present a simple theory that predicts the characteristic actuation frequency. The analysis demonstrates the importance of the native oxide on silicon actuator response, and suggests that the actuation frequency can be shifted by controlling the thickness of the oxide. For native silicon devices, actuation is predicted at frequencies less than 10 MHz, in electrolytes of ionic strength up to 100 mmol/L, and thus electrostatic actuation may be feasible in many bioMEMS and other microfluidic applications.
Characterizing the geology, geotechnical aspects, and rock properties of deep underground facility sites can enhance targeting strategies for both nuclear and conventional weapons. This report describes the results of a study to investigate the utility of remote spectral sensing for augmenting the geological and geotechnical information provided by traditional methods. The project primarily considered novel exploitation methods for space-based sensors, which allow clandestine collection of data from denied sites. The investigation focused on developing and applying novel data analysis methods to estimate geologic and geotechnical characteristics in the vicinity of deep underground facilities. Two such methods, one for measuring thermal rock properties and one for classifying rock types, were explored in detail. Several other data exploitation techniques, developed under other projects, were also examined for their potential utility in geologic characterization.
As rapid Internet growth continues, global communications becomes more dependent on Internet availability for information transfer. Recently, the Internet Engineering Task Force (IETF) introduced a new protocol, Multiple Protocol Label Switching (MPLS), to provide high-performance data flows within the Internet. MPLS emulates two major aspects of the Asynchronous Transfer Mode (ATM) technology. First, each initial IP packet is 'routed' to its destination based on previously known delay and congestion avoidance mechanisms. This allows for effective distribution of network resources and reduces the probability of congestion. Second, after route selection each subsequent packet is assigned a label at each hop, which determines the output port for the packet to reach its final destination. These labels guide the forwarding of each packet at routing nodes more efficiently and with more control than traditional IP forwarding (based on complete address information in each packet) for high-performance data flows. Label assignment is critical in the prompt and accurate delivery of user data. However, the protocols for label distribution were not adequately secured. Thus, if an adversary compromises a node by intercepting and modifying, or more simply injecting false labels into the packet-forwarding engine, the propagation of improperly labeled data flows could create instability in the entire network. In addition, some Virtual Private Network (VPN) solutions take advantage of this 'virtual channel' configuration to eliminate the need for user data encryption to provide privacy. VPN's relying on MPLS require accurate label assignment to maintain user data protection. This research developed a working distributive trust model that demonstrated how to deploy confidentiality, authentication, and non-repudiation in the global network label switching control plane. Simulation models and laboratory testbed implementations that demonstrated this concept were developed, and results from this research were transferred to industry via standards in the Optical Internetworking Forum (OIF).
Coilguns have demonstrated their capability to launch projectiles to 1 km/s, and there is interest in their application for long-range precision strike weapons. However, the incorporation of cooling systems for repetitive operation will impact the mechanical design and response of the future coils. To assess the impact of such changes, an evaluation of the ruggedness and reliability of the existing 50 mm bore coil designed in 1993 was made by repeatedly testing at stress levels associated with operation in a coilgun. A two-coil testbed has been built with a static projectile where each coil is energized by its own capacitor bank. Simulation models of the applied forces generated in this testbed have been created with the SLINGSHOT circuit code to obtain loads equivalent to the worst-case anticipated in a 50 mm coilgun that could launch a 236 g projectile to 2 km/s. Bench measurements of the seven remaining coils built in 1993 have been used to evaluate which coils were viable for testing, and only one was found defective. Measurements of the gradient of the effective coil inductance in the presence of the projectile were compared to values from SLINGSHOT, and the agreement is excellent. Repeated testing of the HFC5 coil built in 1993 has demonstrated no failures after 205 shots, which is an order of magnitude greater than any number achieved in previous testing. Although this testing has only been done on two coils, the results are encouraging as it demonstrates there are no fundamental weak links in the design that will cause a very early failure. Several recommendations for future coil designs are suggested based on observations of this study.
Spectral Dynamics announced the shipment of a 316-channel data acquisition system. The system was custom designed for the Light Initiated High Explosive (LIHE) facility at Sandia Labs in Albuquerque, New Mexico by Spectral Dynamics Advanced Research Products Group. This Spectral Dynamics data acquisition system was tailored to meet the unique LIHE environmental and testing requirements utilizing Spectral Dynamics commercial off the shelf (COTS) Jaguar and VIDAS products supplemented by SD Alliance partner's (COTS) products. 'This system is just the beginning of our cutting edge merged technology solutions,' stated Mark Remelman, Manager for the Spectral Dynamics Advanced Research Products Group. 'This Hybrid system has 316-channels of data acquisition capability, comprised of 102.4kHz direct to disk acquisition and 2.5MHz, 200Mhz & 500Mhz RAM based capabilities. In addition it incorporates the advanced bridge conditioning and dynamic configuration capabilities offered by Spectral Dynamics new Smart Interface Panel System (SIPS{trademark}).' After acceptance testing, Tony King, the Instrumentation Engineer facilitating the project for the Sandia LIHE group commented; 'The LIHE staff was very impressed with the design, construction, attention to detail and overall performance of the instrumentation system'. This system combines VIDAS, a leading edge fourth generation SD-VXI hardware and field-proven software system from SD's Advanced Research Products Group with SD's Jaguar, a multiple Acquisition Control Peripheral (ACP) system that allows expansion to hundreds of channels without sacrificing signal processing performance. Jaguar incorporates dedicated throughput disks for each ACP providing time streaming to disk at up to the maximum sample rate. Spectral Dynamics, Inc. is a leading worldwide supplier of systems and software for advanced computer-automated data acquisition, vibration testing, structural dynamics, explosive shock, high-speed transient capture, acoustic analysis, monitoring, measurement, control and backup. Spectral Dynamics products are used for research, design verification, product testing and process improvement by manufacturers of all types of electrical, electronic and mechanical products, as well as by universities and government-funded agencies. The Advanced Research Products Group is the newest addition to the Spectral Dynamics family. Their newest VXI data acquisition hardware pushes the envelope on capabilities and embodies the same rock solid design methodologies, which have always differentiated Spectral Dynamics from its competition.
The production of metal vapor as a consequence of high intensity laser irradiation is a serious concern in laser welding. Despite the widespread use of lasers in manufacturing, little fundamental understanding of laser/material interaction in the weld pool exists. Laser welding experiments on 304 stainless steel have been completed which have advanced our fundamental understanding of the magnitude and the parameter dependence of metal vaporization in laser spot welding. Calculations using a three-dimensional, transient, numerical model were used to compare with the experimental results. Convection played a very important role in the heat transfer especially towards the end of the laser pulse. The peak temperatures and velocities increased significantly with the laser power density. The liquid flow is mainly driven by the surface tension and to a much less extent, by the buoyancy force. Heat transfer by conduction is important when the liquid velocity is small at the beginning of the pulse and during weld pool solidification. The effective temperature determined from the vapor composition was found to be close to the numerically computed peak temperature at the weld pool surface. At very high power densities, the computed temperatures at the weld pool surface were found to be higher than the boiling point of 304 stainless steel. As a result, vaporization of alloying elements resulted from both total pressure and concentration gradients. The calculations showed that the vaporization was concentrated in a small region under the laser beam where the temperature was very high.
The National Nanotechnology Initiative (NNI), first announced in 1999 has grown into a major U. S. investment involving twenty federal agencies. As a lead federal agency, the Department of Energy (DOE) is developing a network of Nanoscale Science and Research Centers (NSRC). NSRCs will be highly collaborative national user facilities associated with DOE National Laboratories where university, laboratory, and industrial researchers can work together to advance nanoscience and technology. The Center for Integrated Nanotechnologies (CINT), which is operated jointly by Sandia National Laboratories and Alamos National Laboratory, has a unique technical vision focused on integrating scientific disciplines and expertise across multiple length scales going all the way from the nano world to the world around us. It is often said that nanotechnology has the potential to change almost everything we do. However, this prophecy will only come to pass when we learn to couple nanoscale functions into the macroscale world. Obviously coupling the nano- and micro-length scales is an important piece of this challenge and one can site many examples where the performance of existing microdevices has been improved by adding nanotechnology. Examples include low friction coatings for MEMS and compact light sources for ChemLab spectrometers. While this approach has produced significant benefit, we believe that the true potential will be realized only when device architectures are designed 'from the nanoscale up', allowing nanoscale function to drive microscale performance.
Over the past ten years, Sandia has developed RF radar responsive tag systems and supporting technologies for various government agencies and industry partners. RF tags can function as RF transmitters or radar transponders that enable tagging, tracking, and location determination functions. Expertise in tag architecture, microwave and radar design, signal analysis and processing techniques, digital design, modeling and simulation, and testing have been directly applicable to these tag programs. In general, the radar responsive tag designs have emphasized low power, small package size, and the ability to be detected by the radar at long ranges. Recently, there has been an interest in using radar responsive tags for Blue Force tracking and Combat ID (CID). The main reason for this interest is to allow airborne surveillance radars to easily distinguish U.S. assets from those of opposing forces. A Blue Force tracking capability would add materially to situational awareness. Combat ID is also an issue, as evidenced by the fact that approximately one-quarter of all U.S. casualties in the Gulf War took the form of ground troops killed by friendly fire. Because the evolution of warfare in the intervening decade has made asymmetric warfare the norm rather than the exception, swarming engagements in which U.S. forces will be freely intermixed with opposing forces is a situation that must be anticipated. Increasing utilization of precision munitions can be expected to drive fires progressively closer to engaged allied troops at times when visual de-confliction is not an option. In view of these trends, it becomes increasingly important that U.S. ground forces have a widely proliferated all-weather radar responsive tag that communicates to all-weather surveillance. The purpose of this paper is to provide an overview of the recent, current, and future radar responsive research and development activities at Sandia National Laboratories that support both the Blue Force Tracking and Combat ID application.
Alumina/poly(methyl methacrylate) (PMMA) nanocomposites were synthesized using 38 and 17 nm alumina nanoparticles. At an optimum weight fraction, the resulting nanocomposites display a room-temperature brittle-to-ductile transition in uniaxial tension with an increase in the strain-to-failure that averages 40% strain and the appearance of a well-defined yield point in uniaxial tension. Concurrently, the glass transition temperature (T{sub g}) of the nanocomposites drops by more than 20 C. The brittle-to-ductile transition is found to depend on poor interfacial adhesion between polymer and nanoparticle. This allows the nucleation of voids, typically by larger particles ({approx}100 nm), which subsequently expand during loading. This void formation suppresses craze formation and promotes delocalized shear yielding. In addition, the reduction in T{sub g} shrinks the shear yield envelope, further promoting this type of yield behavior. The brittle-to-ductile phenomenon is found to require both larger particles for void growth and smaller particles that induce the lowering of yield stress.
Nanoparticles have received much attention and have been the subject of many reviews. Nanoparticles have also been used to form super molecular structures for molecular electronic, and sensor applications. However, many limitations exist when using nanoparticles, including the ability to manipulate the particles post synthesis. Current methods to prepare nanoparticles employ functionalities like thiols, amines, phosphines, isocyanides, or a citrate as the metal capping agent. While these capping agents prevent agglomeration or precipitation of the particles, most are difficult to displace or impede packing in nanoparticle films due to coulombic repulsion. It is in this vein that we undertook the synthesis of nanoparticles that have a weakly bound capping agent that is strong enough to prevent agglomeration and in the case of the platinum particles allow for purification, but yet, easily displaced by other strongly binding ligands. The nanoparticles where synthesized according to the Brust method except stearonitrile was used instead of an aliphatic thiol. Both platinum and gold were examined in this manner. A representative procedure for the synthesis of platinum nanoparticles involved the phase transfer of chloroplatinic acid (0.37 g, 0.90 mmol) dissolved in water (30 mL) to a solution of tetraoctylammonium bromide (2.2 g, 4.0 mmol) in toluene (80 mL). After the chloroplatinic acid was transferred into the organic phase the aqueous phase was removed. Stearonitrile (0.23 g, 0.87 mmol) was added and sodium borohydride (0.38 g, 49 mmol) in water (25 mL) was added. The solution turned black almost immediately and after 15 min the organic phase was separated and passed through a 0.45 {micro}m Teflon filter. The resulting solution was concentrated and twice precipitated into ethanol ({approx}200 mL) to yield 0.11 g of black platinum nanoparticles. TGA experiments showed that the Pt particles contained 35% by mass stearonitrile. TEM images showed an average particle size of 1.3 {+-} 0.3 nm. A representative procedure for the synthesis of gold nanoparticles involved the transfer of hydrogen tetrachloroaurate (0.18 g, 0.53 mmol) dissolved in water (15 mL) to a solution of tetraoctylammonium bromide (1.1 g, 2.0 mmol) in toluene (40 mL). After the gold salt transferred into the organic phase the aqueous phase was removed. Stearonitrile (0.23 g, 0.87 mmol) was added and sodium borohydride (0.19 g, 5.0 mmol) in water (13 mL) was added. The solution turned dark red almost immediately, and after 15 min the organic phase was separated and passed through a 0.45 {micro}m Teflon filter. The resulting solution was used without purification via precipitation because attempts at precipitation with ethanol resulted in agglomeration. TEM images showed an average particle size of 5.3 {+-} 1.3 nm. The nanoparticles synthesized were also characterized using atomic force microscopy in tapping mode. The AFM images agree with the TEM images and show a relatively monodispersed collection of nanoparticles. Platinum nanoparticles were synthesized without stearonitrile to show that the particles were in fact capped with the stearonitrile and not the tetraoctylammonium bromide. In the absence of stearonitrile the nanoparticles would not redissolve in hexane or toluene after precipitation. While it is possible the tetraoctylammonium bromide helps prevent agglomeration by solvation into the capping stearonitrile ligand layer on the particles recovery of a quantitative amount of the starting tetraoctylammonium bromide was difficult and we cannot rule out that some small amount of tetraoctylammonium bromide serves in a synergistic capacity to help solubilize the isolated platinum particles. Several exchange reactions were carried out using the isolated Pt nanoparticles. The stearonitrile cap was exchanged for hexadecylmercaptan, octanethiol, and benzeneethylthiol. In a typical exchange reaction, Pt nanoparticles (10 mg) were suspended in hexane (10 mL) and the exchange ligand was added (50 {micro}L). The solutions were allowed to stir overnight and precipitated twice using ethanol. TGA experiments confirmed ligand exchange. We have also shown that these particles may be assembled in a layer by layer (LBL) fashion to build up three dimensional assemblies. As an example of this LBL assembly a substrate consisting of gold electrodes separated by 8 {micro}m on a quartz wafer was first functionalized by immersing in a solution of 1,8-octanedithiol (50 {micro}L) in hexane (10 mL) for 15 min, rinsed with hexane (10 mL), ethanol (10 mL), and dried under a stream of nitrogen. The scaffold was then placed in a toluene solution containing Au nanoparticles capped with stearonitrile (10 mg/mL) for 15 minutes. The scaffold was then rinsed with hexane (10 mL), ethanol (10 mL), and dried under a stream of nitrogen. The substrate was then immersed iteratively between the 1,8-octanedithiol and the Au nanoparticle solution 4 more times.
Implicit time integration coupled with SUPG discretization in space leads to additional terms that provide consistency and improve the phase accuracy for convection dominated flows. Recently, it has been suggested that for small Courant numbers these terms may dominate the streamline diffusion term, ostensibly causing destabilization of the SUPG method. While consistent with a straightforward finite element stability analysis, this contention is not supported by computational experiments and contradicts earlier Von-Neumann stability analyses of the semidiscrete SUPG equations. This prompts us to re-examine finite element stability of the fully discrete SUPG equations. A careful analysis of the additional terms reveals that, regardless of the time step size, they are always dominated by the consistent mass matrix. Consequently, SUPG cannot be destabilized for small Courant numbers. Numerical results that illustrate our conclusions are reported.
To observe the effects of polarization fields and screening, we have performed contacted electroreflectance (CER) measurements on In{sub 0.07}Ga{sub 0.93}N/GaN single quantum well light emitting diodes for different reverse bias voltages. Room-temperature CER spectra exhibited three features which are at lower energy than the GaN band gap and are associated with the quantum well. The position of the lowest-energy experimental peak, attributed to the ground-state quantum well transition, exhibited a limited Stark shift except at large reverse bias when a redshift in the peak energy was observed. Realistic band models of the quantum well samples were constructed using self-consistent Schroedinger-Poisson solutions, taking polarization and screening effects in the quantum well fully into account. The model predicts an initial blueshift in transition energy as reverse bias voltage is increased, due to the cancellation of the polarization electric field by the depletion region field and the associated shift due to the quantum-confined Stark effect. A redshift is predicted to occur as the applied field is further increased past the flatband voltage. While the data and the model are in reasonable agreement for voltages past the flatband voltage, they disagree for smaller values of reverse bias, when charge is stored in the quantum well, and no blueshift is observed experimentally. To eliminate the blueshift and screen the electric field, we speculate that electrons in the quantum well are trapped in localized states.
The high-pressure response of cryogenic liquid deuterium (LD{sub 2}) has been studied to pressures of {approx}400GPa and densities of {approx}1.5g/cm{sup 3}. Using intense magnetic pressure produced by the Sandia National Laboratories Z accelerator, macroscopic aluminum or titanium flyer plates, several mm in lateral dimensions and a few hundred microns in thickness, have been launched to velocities in excess of 22 km/s, producing constant pressure drive times of approximately 30 ns in plate impact, shock wave experiments. This flyer plate technique was used to perform shock wave experiments on LD{sub 2} to examine its high-pressure equation of state. Using an impedance matching method, Hugoniot measurements of LD{sub 2} were obtained in the pressure range of {approx}22-100GPa. Results of these experiments indicate a peak compression ratio of approximately 4.3 on the Hugoniot. In contrast, previously reported Hugoniot states inferred from laser-driven experiments indicate a peak compression ratio of approximately 5.5-6 in this same pressure range. The stiff Hugoniot response observed in the present impedance matching experiments was confirmed in simultaneous, independent measurements of the relative transit times of shock waves reverberating within the sample cell, between the front aluminum drive plate and the rear sapphire window. The relative timing was found to be sensitive to the density compression along the principal Hugoniot. Finally, mechanical reshock measurements of LD{sub 2} using sapphire, aluminum, and {alpha}-quartz anvils were made. These results also indicate a stiff response, in agreement with the Hugoniot and reverberating wave measurements. Using simple model-independent arguments based on wave propagation, the principal Hugoniot, reverberating wave, and sapphire anvil reshock measurements are shown to be internally self-consistent, making a strong case for a Hugoniot response with a maximum compression ratio of {approx}4.3-4.5. The trends observed in the present data are in very good agreement with several ab initio models and a recent chemical picture model for LD{sub 2}, but in disagreement with previously reported laser-driven shock results. Due to this disagreement, significant emphasis is placed on the discussion of uncertainties, and the potential systematic errors associated with each measurement.
The US Enabling Technology Program in fusion is investigating the use of free flowing liquid surfaces facing the plasma. We have been studying the issues in integrating a liquid surface divertor into a configuration based upon an advanced tokamak, specifically the ARIES-RS configuration. The simplest form of such a divertor is to extend the flow of the liquid first wall into the divertor and thereby avoid introducing additional fluid streams. In this case, one can modify the flow above the divertor to enhance thermal mixing. For divertors with flowing liquid metals (or other electrically conductive fluids) MHD (magneto-hydrodynamics) effects are a major concern and can produce forces that redirect flow and suppress turbulence. An evaluation of Flibe (a molten salt) as a working fluid was done to assess a case in which the MHD forces could be largely neglected. Initial studies indicate that, for a tokamak with high power density, an integrated Flibe first wall and divertor does not seem workable. We have continued work with molten salts and replaced Flibe with Flinabe, a mixture of lithium, sodium and beryllium fluorides, that has some potential because of its lower melting temperature. Sn and Sn-Li have also been considered, and the initial evaluations on heat removal with minimal plasma contamination show promise, although the complicated 3D MHD flows cannot yet be fully modeled. Particle pumping in these design concepts is accomplished by conventional means (ports and pumps). However, trapping of hydrogen in these flowing liquids seems plausible and novel concepts for entrapping helium are also being studied.
Low temperature, Sn-based Pb-free solders were developed by making alloy additions to the starting material, 96.5Sn-3.5Ag (mass%). The melting behavior was determined using Differential Scanning Calorimetry (DSC). The solder microstructure was evaluated by optical microscopy and electron probe microanalysis (EPMA). Shear strength measurements, hardness tests, intermetallic compound (IMC) layer growth measurements, and solderability tests were performed on selected alloys. Three promising ternary alloy compositions and respective solidus temperatures were: 91.84Sn-3.33Ag-4.83Bi, 212 C; 87.5Sn-7.5Au-5.0Bi, 200 C; and 86.4Sn-5.1 Ag-8.5Au, 205 C. A quaternary alloy had the composition 86.8Sn-3.2Ag-5.0Bi-5.0Au and solidus temperature of 194 C The shear strength of this quaternary alloy was nearly twice that of the eutectic Sn-Pb solder. The 66Sn-5.0Ag-10Bi-5.0Au-101n-4.0Cu alloy had a solidus temperature of 178 C and good solderability on Cu. The lowest solidus temperature of 159 C was realized with the alloy 62Sn-5.0Ag-10Bi-4.0Au-101n-4.0Cu-5.0Ga. The contributing factor towards the melting point depression was the composition of the solid solution, Sn-based matrix phase of each solder.
Within the magnetic fusion energy program in the US, a program called APEX is investigating the use of free flowing liquid surfaces to form the inner surface of the chamber around the plasma. As part of this work, the APEX Team has investigated several possible design implementations and developed a specific engineering concept for a fusion reactor with liquid walls. Our approach has been to utilize an already established design for a future fusion reactor, the ARIES-RS, for the basic chamber geometry and magnetic configuration, and to replace the chamber technology in this design with liquid wall technology for a first wall and divertor and a blanket with adequate tritium breeding. This paper gives an overview of one design with a molten salt (a mixture of lithium, beryllium and sodium fluorides) forming the liquid surfaces and a ferritic steel for the structural material of the blanket. The design point is a reactor with 3840 MW of fusion power of which 767 MW is in the form of energetic particles (alpha power) and 3073 MW is in the form of neutrons. The alpha plus auxiliary power total 909 MW of which 430 MW is radiated from the core mostly onto the first wall and the balance flows into the edge plasma and is distributed between the first wall and the divertor. In pursuing the application of liquid surfaces in APEX, the team has developed analytical tools that are significant achievements themselves and also pursued experiments on flowing liquids. This work is covered elsewhere, but the paper will also note several such areas to indicate the supporting science behind the design presented. Significant new work in modeling the plasma edge to understand the interaction of the plasma with the liquid walls is one example. Another is the incorporation of magneto-hydrodynamic (MHD) effects in fluid modeling and heat transfer.