Search

Swarms of micro- and milli-sized robots have the potential to advance biological micro-manipulation, micro- assembly and manufacturing, and provide an ideal platform for studying large swarm behaviors and control. Due to their small size and low cost, tens to hundreds of micro/milli robots can function in parallel to perform a task that otherwise would be too cumbersome or costly for a larger macroscopic robot. Here, we demonstrate a scalable system and modular circuit architecture for controlling and coordinating the motion of $ >$ 10's of magnetic micro/milli robots. By modifying the concepts of safety barrier certificates to our magnetic robot hardware, we achieve minimally invasive, collision-free, 2D position control (x, y) of up to N = 16 robots in a low-cost tabletop ( $\text{288 mm} \times \text{288 mm}$ ) magnetic milli-robot platform with up to 288 degrees of freedom. We show that the introduction of random dithering can achieve a $100\%$ success rate (i.e., no deadlocking), enabling the system to serve as a platform for the study of various swarm-like behaviors or multi-agent robotic coordination.

Neutralizing antibodies targeting the SARS-CoV-2 spike protein have shown a great preventative/therapeutic potential. Here, we report a rapid and efficient strategy for the development and design of SARS-CoV-2 neutralizing humanized nanobody constructs with sub-nanomolar affinities and nanomolar potencies. CryoEM-based structural analysis of the nanobodies in complex with spike revealed two distinct binding modes. The most potent nanobody, RBD-1-2G(NCATS-BL8125), tolerates the N501Y RBD mutation and remains capable of neutralizing the B.1.1.7 (Alpha) variant. Molecular dynamics simulations provide a structural basis for understanding the neutralization process of nanobodies exclusively focused on the spike-ACE2 interface with and without the N501Y mutation on RBD. A primary human airway air-lung interface (ALI) ex vivo model showed that RBD-1-2G-Fc antibody treatment was effective at reducing viral burden following WA1 and B.1.1.7 SARS-CoV-2 infections. Therefore, this presented strategy will serve as a tool to mitigate the threat of emerging SARS-CoV-2 variants. ONE-SENTENCE SUMMARY: A cost-effective, high-throughput, adaptable pipeline capable of identifying effective humanized nanobodies against SARS-CoV-2.

Microbiological environments are a clear application area for microscale robotics, but targeted delivery of biochemical cues to particular cells or tissues remains a significant challenge. This challenge is compounded by the sheer number of cells that compose tissues. Multirobot system development has been limited due to challenges in discrete operation of several robots in a confined space. Here, we demonstrate the use of multiple diamagnetically levitated robots for delivering biochemicals dissolved in liquid in a manner compatible with light microscopy. Specifically, we show loading, transport, and diffusive release of fluorescent molecules in hydrogels with microscale precision, as well as induction of synthetically engineered bacterial cells with signaling molecules. This platform holds potential for impact and utility in fields, such as developmental biology, tissue engineering, and synthetic biology.

In this article, we demonstrate diamagnetically levitated milli-robots performing 3D heterogeneous micro-assembly of silicon micro-machined parts and polymer microspheres. Diamagnetically levitated milli-robots, in conjunction with controlled magnetic fields from printed circuit boards, can enable very precise, low cost, high density, and an easily scalable approach to massively parallel micro-assembly. By using an eddy-current dampening layer to suppress ambient external forces, we measured an open-loop in-plane equilibrium motion repeatability of 28.6 nm rms over cm’s of travel and a total vertical range of 50–70 μm. To perform micro-assembly, light-weight end effectors and force compatible micro-processes (i.e. micro-grasping and liquid handling) were integrated with the diamagnetic levitated milli-robots. Various tele-operated micro-assembly tasks were demonstrated such as joining polymer micro-spheres, interlocking silicon micro-parts, and printing electrical interconnects. Multiple specialized milli-robots, each taking up only 31 mm2, are used to perform each individual micro-task. In the future, by developing more sophisticated milli-robots and operating many more of these milli-robots in parallel, a dense, automated, rapid milli-robot assembly may be possible.

Magnetic micro-robots have a variety of potential applications for biomedical manipulation and microassembly. However, providing independent degrees of freedom to individual magnetic micro-robots can be hindered by the large numbers of local coils or traces required to achieve all degrees of freedom. In this paper, we explore the use of novel control strategies and mechanical constraints to provide additional rotational degrees of freedom to underactuated multipole magnetic robots originally designed with only translational degrees of freedom. By carefully applying repulsive impulse forces and changing the center of rotation, we show that a dynamic in-plane rotation of 3500 deg/s can be achieved. By using other geometries of mechanical constraints such as a wheel on axle, we can also demonstrate 1800 deg/s out-of-plane rotation.

Diverse parallel stitched 2D heterostructures, including metal–semiconductor, semiconductor–semiconductor, and insulator–semiconductor, are synthesized directly through selective “sowing” of aromatic molecules as the seeds in the chemical vapor deposition (CVD) method. The methodology enables the large-scale fabrication of lateral heterostructures, which offers tremendous potential for its application in integrated circuits., Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Award No. 023674), National Science Foundation (U.S.). Division of Materials Research. (Award No. 1004147), United States. Department of Energy. (Award No. DE-SC0001299), United States. Office of Naval Research. Presidential Early Career Award for Scientists and Engineers (Award No. 021302-001), United States. Department of Energy. (Contract No. DE-AC02-98CH10886), China. Ministry of Science and Technology. (MOST 103-2112-M-007-001-MY3)

In this article, we study the use of ferrofluids for levitating magnetic micro/milli-robots. With the addition of a ferrofluid, the robots improved their weight-carrying ability (xI2, >12 grams) and precision (x2 ~5 um) without any associated increase in actuation power of the robot relative to sliding versions without the ferrofluid. To better understand the longterm stability of a ferrofluid on the micro/milli-robot, we perform motion cycle testing on two different surfaces (graphite and Teflon), ultimately achieving a motion repeatability and pose angular stability of 5 um and 0.05 °, close to the limits of our measurement setup. The underdamped motion of the ferrofluid robot showed a natural resonance of ~58–60 Hz. Through careful control of the evaporation of the ferrofluid, we show long-term stability of a ferrofluid micro/milli-robot over the course of >11 hours. While the performance of the robot does change due to evaporation of the particular ferrofluid used, we also show that robots can easily be replenished with new ferrofluid after mechanically cleaning away the remaining ferrofluid. Overall, the application of ferrofluids toward magnetically actuated micro/milli-robots can enable low-cost and high-precision motion for future high-precision micro-manipulation or positioning tasks.

In this work, we leverage graphene's unique tunable Seebeck coefficient for the demonstration of a graphene-based thermal imaging system. By integrating graphene based photothermo-electric detectors with micromachined silicon nitride membranes, we are able to achieve room temperature responsivities on the order of ~7-9 V/W (at λ = 10.6 μm), with a time constant of ~23 ms. The large responsivities, due to the combination of thermal isolation and broadband infrared absorption from the underlying SiN membrane, have enabled detection as well as stand-off imaging of an incoherent blackbody target (300-500 K). By comparing the fundamental achievable performance of these graphene-based thermopiles with standard thermocouple materials, we extrapolate that graphene's high carrier mobility can enable improved performances with respect to two main figures of merit for infrared detectors: detectivity (>8 × 10(8) cm Hz(1/2) W(-1)) and noise equivalent temperature difference (

In this article, we demonstrate the application of diamagnetically levitated milli-robots for the 2D micro-assembly of 10-μm polymer microspheres and other silicon microfabricated parts. By using an optical microscope for feedback (imaged at 27 Hz), we are able to demonstrate long-term open-loop stability (up to 78 hr) and sub-micron stability of the levitated micro-robots. Furthermore, due to the low hysteresis and high compliance in the magnetic drive of the milli-robots, we are able to directly use the milli-robots in conjunction with machine vision as a force sensor. Soft polymer-based end effectors are used for the micromanipulation of parts and show modest reliability of pick (>70%) and high reliability of place (>99%) that is insensitive to the pick surface material. Finally, we implement autonomous micro-assembly from randomly deposited microspheres into ordered arrays.

Multi-agent robotic systems on small scales typically use, or envision using, small mobile robots. This paper takes a broad-brush look at a relatively recent development in milli and micro robots, Diamagnetic Micro Manipulation (DM3) systems, in a multi-agent context. We report various multi-agent operations, such as multi-agent part manipulation, robots-acting-on-other-robots for enhanced functionality, and robot-supplied local feed, to assess the state of the art of this new type of system. In addition, we explore and analyze the multi-agent implications of known DM3 properties and earlier single-agent results to motivate future research in this area. As reported here, some of these multi-agent implications include mobile high-precision sensor transducers, near-field communications channels using robots as both transmitters and receivers, and novel swarm architectures.

This paper presents a model for graphene electrolyte-gated field-effect transistors (EGFETs) that incorporates the effects of the graphene-electrolyte interface and quantum capacitance of graphene. The model is validated using experimental data collected from fabricated graphene EGFETs and is employed to extract device parameters such as mobility, minimum carrier concentration, interface capacitance, contact resistance, and effective charged impurity concentration. The proposed graphene EGFET model accurately determines a number of properties necessary for circuit design, such as current-voltage characteristics, transconductance, output resistance, and intrinsic gain. The model can also be used to optimize the design of EGFETs. For example, simulated and experimental results show that avoiding the practice of partial channel passivation enhances the transconductance of graphene EGFETs.

Photoluminescence (PL) properties of single-layer MoS2 are indicated to have strong correlations with the surrounding dielectric environment. Blue shifts of up to 40 meV of exciton or trion PL peaks were observed as a function of the dielectric constant of the environment. These results can be explained by the dielectric screening effect of the Coulomb potential; based on this, a scaling relationship was developed with the extracted electronic band gap and exciton and trion binding energies in good agreement with theoretical estimations. It was also observed that the trion/exciton intensity ratio can be tuned by at least 1 order of magnitude with different dielectric environments. Our findings are helpful to better understand the tightly bound exciton properties in strongly quantum-confined systems and provide a simple approach to the selective and separate generation of excitons or trions with potential applications in excitonic interconnects and valleytronics.

In this work, we investigated the growth mechanisms of bilayer graphene on the outside surface of Cu enclosures at low pressures. We observed that the asymmetric growth environment of a Cu enclosure can yield a much higher (up to 100%) bilayer coverage on the outside surface as compared to the bilayer growth on a flat Cu foil, where both sides are exposed to the same growth environment. By simultaneously examining the graphene films grown on both the outside and inside surfaces of the Cu enclosure, we find that carbon can diffuse from the inside surface to the outside via exposed copper regions on the inside surface. The kinetics of this process are examined by coupling the asymmetric growth between the two surfaces through a carbon diffusion model. Finally, using these results, we show that the coverage of bilayer graphene can be tuned simply by changing the thickness of the Cu foil, further confirming our model of carbon delivery through the Cu foil.

We explore the photoresponse of an ambipolar graphene infrared thermocouple at photon energies close to or below monolayer graphene's optical phonon energy and electrostatically accessible Fermi energy levels. The ambipolar graphene infrared thermocouple consists of monolayer graphene supported by an infrared absorbing material, controlled by two independent electrostatic gates embedded below the absorber. Using a scanning infrared laser microscope, we characterize these devices as a function of carrier type and carrier density difference controlled at the junction between the two electrostatic gates. On the basis of these measurements, conducted at both mid- and near-infrared wavelengths, the primary detection mechanism can be modeled as a thermoelectric response. By studying the effect of different infrared absorbers, we determine that the optical absorption and thermal conduction of the substrate play the dominant role in the measured photoresponse of our devices. These experiments indicate a path toward hybrid graphene thermal detectors for sensing applications such as thermography and chemical spectroscopy.

We systematically investigated plasma-based chlorination of graphene and compared its properties before and after such treatment. X-ray photoelectron spectroscopy revealed that a high Cl coverage of 45.3% (close to C2Cl), together with a high mobility of 1535 cm(2)/(V s), was achieved. The C:Cl ratio n (CnCl) can be effectively tuned by controlling the dc bias and treatment time in the plasma chamber. Chlorinated graphene field-effect transistors were fabricated, and subsequent Hall-effect measurements showed that the hole carrier concentration in the chlorinated graphene can be increased roughly by a factor of 3. Raman spectra indicated that the bonding type between Cl and graphene depends sensitively on the dc bias applied in the plasma chamber during chlorination and can therefore be engineered into different reaction regimes, such as ionic bonding, covalent bonding, and defect creation. Micro-Raman mapping showed that the plasma-based chlorination process is a uniform process on the micrometer scale.

Recent experiments since the discovery of monolayer graphite or graphene have led to an exciting revival in the interest in the electronic applications for graphene, as well as other 2-D materials such as hexagonal boron nitride (hBN) and molybdenum disulfide (MoS2). These layered materials serve as an exciting new platform for flexible and transparent electronics where surfaces can be enriched with new functionality. This paper aims to provide an overview behind these new class of materials ranging upon important issues for electronic integration including synthesis all the way to current state-of-the-art circuits and devices made from these materials.

Two-dimensional (2D) materials such as graphene and hexagonal boron nitride (hBN) have attracted significant attention due to their remarkable properties. Numerous interesting graphene/hBN hybrid structures have been proposed but their implementation has been very limited. In this work, the synthesis of patched structures through consecutive chemical vapor deposition (CVD) on the same substrate was investigated. Both in-plane junctions and stacked layers were obtained. For stacked layers, depending on the synthesis sequence, in one case turbostratic stacking with random rotations were obtained. In another, "AA-like", slightly twisted stacking between graphene and hBN was observed with lattice orientation misalignment consistently to be1°. Raman characterizations not only confirmed that hBN is a superior substrate but also revealed for the first time that a graphene edge with hBN passivation displays reduced D band intensity compared to an open edge. These studies pave the way for the proposed well-ordered graphene/hBN structures and outline exciting future directions for hybrid 2D materials.

Today, trends in manufacturing automation favor high levels of adaptability and flexibility for rapid product change, customization, and new process integration. This paper looks at a new technology, diamagnetic micro manipulation (DM3), for taking adaptability of automation to a higher level. Experiments reported here show a path to automation systems that can self-assemble their own robotic manipulators, fabricate tools-on-demand to execute new processes, optimize existing processes, and/or replace or repair tools. These printed circuit board (PCB) systems can control very large numbers of milli-scale robots. Hence, as described in this paper and in contrast to conventional robotic systems, only a small percentage of DM3 system resources, approximately 5–10% of system area and robot numbers, are needed to achieve on-board self-assembly and tool-on-demand functions. This paper describes the key step of self-assembly of self-levitating magnet arrays using 1 mm × 1 mm × 0.4 mm magnets, with self-assembly times of less than 10 s. We also report experiments showing how milli-robots can build simple end effector tools (a straight probe tip, a forked tip, and a hook tip) on other milli-robots for on-board, tool-on-demand functions.

This paper reports early results of optimal control using diamagnetically levitated robot (DLR) systems. Levitated robots, typically 1–4 mm in size, are driven locally by printed circuit boards (PCBs) with zero friction and near-zero hysteresis. As previously reported [1, 2], these properties give the levitated system excellent repeatability at the micron and submicron levels for both positioning and trajectories. Highly repeatable systems are generally good candidates for optimal control because variability in identifying and exploiting optimized control parameters are minimized. In the data reported here, levitated milli robots are characterized, and we present experiments showing a 5× reduction in oscillations using a debouncing routine that is manually optimized in time. Manual optimization is effective in some cases, but due to the multi-degree-of-freedom (DOF) aspects of levitated robots, a more robust self-tuning method is desirable. Toward this goal, we describe experiments using automatic optimization of robot motion using a computerized search-and-test routine that varies PCB trace currents and selects optimal currents based on automatic measurement of motion error. The automatic optimization using this method has shown settling times to micron and submicron levels that are 20–40 times faster than simple bang-bang control of equilibrium currents. In one test reported here, 150-µm moves were demonstrated at 90-nm rms error with 15-ms move times.

Using diamagnetic micro-manipulation, micro-robots (∼10 mm in size) with specialized end-effectors are able to grasp and manipulate small light weight (∼mg) carbon fiber elements to construct macroscopic cubic carbon fiber trusses (∼1000 parts and 300 mm long) that can achieve mechanical crush performances surpassing those of commercially available aluminum honey combs. Employing low cost micro-robots and end-effectors allows the implementation of both parallelization and new functionality without the need for expensive fixed tooling. We demonstrate this concept by modifying the micro-robot end effectors to build carbon fiber octet trusses and carbon fiber trusses with integrated electronics.

We present a method for synthesizing MoS2/Graphene hybrid heterostructures with a growth template of graphene-covered Cu foil. Compared to other recent reports,(1, 2) a much lower growth temperature of 400 °C is required for this procedure. The chemical vapor deposition of MoS2 on the graphene surface gives rise to single crystalline hexagonal flakes with a typical lateral size ranging from several hundred nanometers to several micrometers. The precursor (ammonium thiomolybdate) together with solvent was transported to graphene surface by a carrier gas at room temperature, which was then followed by post annealing. At an elevated temperature, the precursor self-assembles to form MoS2 flakes epitaxially on the graphene surface via thermal decomposition. With higher amount of precursor delivered onto the graphene surface, a continuous MoS2 film on graphene can be obtained. This simple chemical vapor deposition method provides a unique approach for the synthesis of graphene heterostructures and surface funct...

The outstanding properties of graphene have attracted intense research activities to take advantage of this new material for improving existing electronic applications and inventing new ones. Some of the target applications include digital and RF electronics, advanced sensors, semitransparent electronics, low power switches, solar cells, and battery energy storage. While the lack of bandgap in graphene imposes serious limitations on its application for digital electronics, many RF circuits do not require the existence of a bandgap and can be realized in devices with a low on-off current ratio. In this article, we review the recent progress in using graphene for applications in RF and mixed-signal circuits, arguably one of the most promising fields for future graphene electronics.

Hexagonal boron nitride (h-BN) is very attractive for many applications, particularly, as protective coating, dielectric layer/substrate, transparent membrane, or deep ultraviolet emitter. In this work, we carried out a detailed investigation of h-BN synthesis on Cu substrate using chemical vapor deposition (CVD) with two heating zones under low pressure (LP). Previous atmospheric pressure (AP) CVD syntheses were only able to obtain few layer h-BN without a good control on the number of layers. In contrast, under LPCVD growth, monolayer h-BN was synthesized and time-dependent growth was investigated. It was also observed that the morphology of the Cu surface affects the location and density of the h-BN nucleation. Ammonia borane is used as a BN precursor, which is easily accessible and more stable under ambient conditions than borazine. The h-BN films are characterized by atomic force microscopy, transmission electron microscopy, and electron energy loss spectroscopy analyses. Our results suggest that the growth here occurs via surface-mediated growth, which is similar to graphene growth on Cu under low pressure. These atomically thin layers are particularly attractive for use as atomic membranes or dielectric layers/substrates for graphene devices.

This paper presents a compact model for the current-voltage characteristics of graphene field-effect transistors (GFETs), which is based on an extension of the “virtual-source” model previously proposed for Si MOSFETs and is valid for both saturation and nonsaturation regions of device operation. This GFET virtual-source model provides a simple and intuitive understanding of carrier transport in GFETs, allowing extraction of the virtual-source injection velocity vVS, which is a physical parameter with great technological significance for short-channel graphene transistors. The derived I-V characteristics account for the combined effects of the drain-source voltage VDS, the top-gate voltage VTGS, and the back-gate voltage VBGS. With only a small set of fitting parameters, the model shows excellent agreement with experimental data. It is also shown that the extracted virtual-source carrier injection velocity for graphene devices is much higher than in Si MOSFETs and state-of-the-art III-V heterostructure FETs with similar gate length, demonstrating the great potential of GFETs for high-frequency applications. Comparison with experimental data for chemical-vapor-deposited GFETs from our group and epitaxial GFETs in the literature confirms the validity and flexibility of the model for a wide range of existing GFET devices.

In this contribution we demonstrate a method of synthesizing a hexagonal boron nitride (h-BN) thin film by ambient pressure chemical vapor deposition on polycrystalline Ni films. Depending on the growth conditions, the thickness of the obtained h-BN film is between ∼5 and 50 nm. The h-BN grows continuously on the entire Ni surface and the region with uniform thickness can be up to 20 μm in lateral size which is only limited by the size of the Ni single crystal grains. The hexagonal structure was confirmed by both electron and X-ray diffraction. X-ray photoelectron spectroscopy shows the B/N atomic ratio to be 1:1.12. A large optical band gap (5.92 eV) was obtained from the photoabsorption spectra which suggest the potential usage of this h-BN film in optoelectronic devices.

Graphene, a one-atom-thick layer of carbon atoms arranged in a honeycomb lattice, has recently attracted great interest among physicists and engineers. The combination of the unique properties of graphene with new device concepts and nanotechnology can overcome some of the main limitations of traditional radio frequency electronics in terms of maximum frequency, linearity, and power dissipation. In this article we review the current status of research on graphene-based electronic devices for RF applications. The future challenges facing this rising technology and its feasibility for a new generation of applications in RF communications and circuits are also discussed.

Strain-compensated (SC) GaInAs/AlInAs/InP multiple-quantum-well structures and quantum cascade lasers (QCLs) with strain levels of 1% and as high as 1.5% were grown by organometallic vapor phase epitaxy (OMVPE). The structures were characterized by high-resolution X-ray (HRXRD) diffraction and atomic force microscopy (AFM), and narrow-ridge QCL devices were fabricated. HRXRD and AFM results indicate very high quality materials with narrow satellite peaks, well-defined interference fringes, and a step-flow growth mode for 1% SC materials. A marginal broadening of satellite peaks is measured for 1.5% SC structures, but step-flow growth is maintained. QCLs based on a conventional four-quantum-well double-phonon resonant active region design with nominal 1% SC were grown with doping concentration varied from 1 to 4×1017 cm−3 in the active region. The performance of ridge lasers under pulsed conditions is comparable to state-of-the-art results for 4.8 μm devices. QCLs with a novel injectorless four-quantum well QCL design and 1.5% SC operated in pulsed mode at room temperature at 5.5 μm.

The elderly constitute an increasing portion of the world's population. Our study assessed morbidity, mortality, and outcome in octogenarians who have undergone lower intestinal operations, and compared outcome between subsequent decades.A total of 138 octogenarians who underwent 157 operations were retrospectively studied (1995-2005). The American Society of Anesthesiologists Physical Status classification, blood loss, length of surgery, surgical intensive care unit admission, length of surgical intensive care unit and hospital stay, and complications were recorded. Emergency vs. elective and cancer vs. noncancer cases were compared. Results were compared for the years 1985 to 1994.Cancer comprised 63 percent of cases. The most common causes of mortality were sepsis and multiorgan failure. Differences (P0.05) were found for elective vs. emergent surgeries according to age, length of stay, complications, surgical intensive care unit admission, American Society of Anesthesiologists Physical Status classification, and mortality. Noncancer cases were more likely to be emergent, have a higher American Society of Anesthesiologists Physical Status classification, and a higher mortality rate. When emergency operations were excluded, there were no significant differences between cancer vs. noncancer cases. In a comparison of two decades (1985-1994 vs. 1995-2005), we found that the mortality rate in patients younger than aged 85 years decreased by more than 10 percent (P0.05). Patients older than aged 85 years demonstrated no significant differences between decades. The strongest determinants of outcome are emergency status and the presence of comorbid conditions.Elective surgery in the elderly is safe. Emergency surgery is accompanied by significant morbidity and mortality.

This study measures the reaction rate of dolomite and aragonite (calcite) into Mg-calcite at 800, 850, and 900°C and 1.6 GPa. The dry synthetic dolomite-aragonite aggregate transformed very rapidly into dolomite-calcite polycrystalline aggregate while Mg-calcites formed at a relatively slow rate, becoming progressively richer in Mg with run time. We modeled the reaction progress semi- empirically by the first-order rate law. The temperature dependence of the overall transport rate of MgCO3 into calcite can be described by the kinetic parameters (E= 231.7 kJ/mol and Ao=22.69 h �1 ). Extrapolation using the Arrhenius equation to the conditions during exhumation of UHPM rocks indicates that the reaction of dolomite with aragonite into Mg-saturated calcite can be completed as the P-T path enters the Mg-calcite stability field in a geologically short time period ( 340°C and >10 My). SEM-EDS analysis of individual calcite grains shows compositional gradients of Mg in the calcite grains. The Mg-Ca inter- diffusion coefficient at 850°C is around 1.68×10 �14 m 2 /sec if diffusion is the major control of the reaction. The calculated closure temperatures for Ca-Mg inter-diffusion as a function of cooling rate and grain size reveal that Ca/Mg resetting in calcite in a dry polycrystalline carbonate aggregate (with grain size around 1 mm) may not occur at temperatures below 480°C at a geological cooling rate around 10°C/My, unless other processes, such as short-circuit interdiffusion along grain boundaries and dislocations, are involved.

Kerogens concentrated from oil-prone source rocks of different depositional environments and macerals isolated from humic coals were characterized using fluorescence microscopy at ambient and elevated temperatures. The initial fluorescence intensities for bulk kerogens ( F initial ) under ambient conditions are correlated with their hydrogen index (HI). Four lacustrine kerogens exhibit much higher maximum fluorescence yields ( F max ) during transformation at elevated temperatures than the marine and terrestrial kerogens. The F initial of these kerogens can be correlated with their F max , and may provide some insight into their oil generation potential. Liptinite isolated from humic coals exhibits both higher F initial and F max , consistent with their higher oil generation potential than vitrinite and fusinite (inertinite). F max of isolated vitrinites shows a positive correlation with their maturity below 1.2%Ro and a negative correlation at higher maturity, implying the decline of their oil generation potentials at high maturity. Green River kerogen (GR) and marinite exhibit prolonged positive temporal fluorescence alteration (TFA) whereas other kerogens and liptinite display only subtle TFA under ambient conditions. The extents of alteration are enhanced by temperatures. TFAs of the GR kerogen in argon relative to that in air at ambient and elevated temperatures are significantly reduced, confirming oxidation accounts for the TFA. The temperature dependence (thermal quenching) of the kerogen between 25 and 200 °C is comparable to crude oils and exhibits hysteresis in the heating or cooling cycle. The present study has demonstrated that the fluorescence of bulk kerogens at elevated temperatures before or during organic transformation can be used to characterize organic matter.

Anterior resection with rectopexy is considered by many to be the best operation for rectal prolapse. It is feared that if sigmoid redundancy created by rectal mobilization is not resected, colonic motility (specifically constipation) could be disabling. We contend that resection is not necessary in patients without preexisting constipation. We tested this hypothesis using a laparoscopic approach to minimize hospital stay. Twelve patients were treated (eight women); mean age was 45 years (range, 25–82 years). No patient had preexisting constipation; one had irritable bowel syndrome. Three patients had prior prolapse operations. Full rectal mobilization was undertaken down to the levator hiatus; neither the mesenteric vessels nor the lateral ligaments were divided. Rectopexy to the presacral fascia was done with one to two Nurolon sutures on either side of the rectum. There were no complications; mean hospital stay was 4 days. Mean follow up was 32 months (range; 3–75 months); there have been no recurrences. Only the patient with irritable bowel syndrome developed significant constipation. We conclude: 1) rectopexy can be safely done laparoscopically, 2) resection is not required in the absence of prior constipation, and 3) rectal mobilization and rectopexy does not predispose to future constipation in these selected patients.

Reversal of a Hartmann's operation can be a morbid undertaking; successful restoration of intestinal continuity cannot be guaranteed. Between June 2001 and July 2006, 35 Hartmann's reversals were undertaken. There were 19 males (54%). Mean age was 54.7 years (range, 14–82 years). Twenty-one (60%) patients had their Hartmann's for diverticular disease, 7 (20%) for anorectal cancer, 4 (11%) for volvulus, and 3 for miscellaneous reasons. Mean length of stay was 7.7 days (range, 3–16 days); 23 per cent required intensive care for a mean 2.3 days (range, 1–4 days). Blood loss was 470 mL, and mean operative time was 4.28 hours (range, 1–8.3 hours). The mean time interval between the original operation and its reversal was 8.9 months (range, 1.4–55 months). Extensive lysis of adhesions was required in 69 per cent, 40 per cent experienced minor complications (urinary tract infections, ileus, and so on), and 38 per cent had major complications (myocardial infarction, leak, hernias, respiratory failure). There was one death (3%). The operation failed because of intraoperative circumstances in three patients (8%). Ten patients (26%) had stomas at the time of discharge of which 3 were intended to be permanent and 7 were temporary. Of the latter, 3 were successfully closed, 3 are awaiting closure, and 1 had complete anastomotic failure requiring permanent diversion. Total failure rate was 10.3 per cent; contributing factors included prior radiation and ultra-low anastomoses.

Bilayer graphene has attracted considerable attention due to its potential as a tunable band gap in AB-stacked bilayers. Recently, great advancements have been made in the synthesis of chemical-vapor-deposited bilayer graphene. This featured article provides a detailed and up-to-date review of the synthesis of bilayer graphene by chemical vapor deposition (CVD). We will discuss various approaches to synthesize bilayer graphene and the corresponding growth dynamics. Methods for identifying the growth mechanism of bilayer graphene on Cu enclosures are highlighted for a deeper understanding of better control over uniformity and thickness.

Although hexagonal boron nitride (h-BN) is a good candidate for gate-insulating materials by minimizing interaction from substrate, further applications to electronic devices with available two-dimensional semiconductors continue to be limited by flake size. While monolayer h-BN has been synthesized on Pt and Cu foil using chemical vapour deposition (CVD), multilayer h-BN is still absent. Here we use Fe foil and synthesize large-area multilayer h-BN film by CVD with a borazine precursor. These films reveal strong cathodoluminescence and high mechanical strength (Young’s modulus: 1.16±0.1 TPa), reminiscent of formation of high-quality h-BN. The CVD-grown graphene on multilayer h-BN film yields a high carrier mobility of ~24,000 cm[superscript 2] V[superscript −1] s[superscript −1] at room temperature, higher than that (~13,000 [superscript 2] V[superscript −1] s[superscript −1]) with exfoliated h-BN. By placing additional h-BN on a SiO[subscript 2]/Si substrate for a MoS[subscript 2] (WSe[subscript 2]) field-effect transistor, the doping effect from gate oxide is minimized and furthermore the mobility is improved by four (150) times., Korea Institute of Science and Technology. Institutional Program, National Science Foundation (U.S.) (STC Center for Integrated Quantum Materials Grant DMR-1231319), Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies

We have found that tungsten (W) foils can be used for controlling the carbon diffusion within copper (Cu) enclosures to synthesize large-domain bi-/multi-layer-free monolayer graphene via chemical vapor deposition. We have observed that bi-/multi-layer graphene that nucleate underneath the monolayer graphene can be selectively removed by a W foil placed inside of the Cu enclosure. Both X-ray photoelectron spectroscopy and X-ray diffraction reveal the formation of tungsten sub-carbide (W2C), suggesting the role of the W foil as a carbon sink that alters the carbon concentration inside of the enclosure. Consequently, the bi-/multi-layers appear to dissolve. Utilizing this selective removal process, we were able to demonstrate large-domain (>200 μm) monolayer graphene that is free of any bi-/multi-layers by using Cu double enclosures.

Graphene, owing to its ability to support plasmon polariton waves in the terahertz frequency range, enables the miniaturization and electrical tunability of antennas to allow wireless communications among nanosystems. One of the main challenges in the characterization and demonstration of graphene antennas is finding suitable terahertz sources to feed the antenna. This paper characterizes the performance of a graphene RF plasmonic antenna fed with a photoconductive source. The terahertz source is modeled and, by means of a full-wave EM solver, the radiated power as well as the tunable resonant frequency of the device is estimated with respect to material, laser illumination, and antenna geometry parameters. The results show that with this setup the antenna radiates terahertz pulses with an average power up to 1 μW and shows promising electrical frequency tunability., United States. Office of Naval Research. Presidential Early Career Awards for Scientists and Engineers, Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies, Spain. Ministerio de Educacion y Ciencia (FPU Grant), Catalonia (Spain) (Grant 2014SGR-1427)

A compact-size circularly polarized antenna is investigated by employing high-permittivity and low-loss substrate (i.e., high Q × f value) for 2.5-GHz application. The antenna was individually fabricated on nano-Al2O3 (er = 9.7, Q × f value of 500,000 GHz) and Al2O3 (er = 9.7, Q × f value of 200,000 GHz) substrates. The high-permittivity and low-loss ceramic substrate (nano-Al2O3 substrate) was used to reduce the microstrip antenna dimension on patch size. In addition, the ceramic substrate was studied for broadening the 3-dB axial ratio bandwidth [circular polarization (CP) bandwidth]. The obtained CP bandwidth is about 80 MHz (∼3.2%) at 2.5 GHz. The proposed antenna occupies a size of 23.4 × 23.4 × 4 mm3 and obtains the operation bandwidth of about 90.96 MHz. Good antenna gain and CP radiation patterns have also been observed. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2317–2320, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21909