Fast Ramp Research Articles

Antibodies@MOFs: An In Vitro Protective Coating for Preparation and Storage of Biopharmaceuticals.

Antibodies have emerged as a fast-growing category of biopharmaceuticals that have been widely applied in scientific research, medical diagnosis, and disease treatment. However, many antibodies and other biopharmaceuticals display inferior biophysical properties, such as low stability and a propensity to undergo aggregation. Enhancing the stability of biopharmaceuticals is essential for their wide applications. Here, a facile in vitro protective coating strategy based on metal-organic frameworks (MOFs) is proposed to efficiently protect antibodies against perturbation environments and quickly recover them from the MOFs before usage, which avoids introducing protective additives into the body, which may cause biosafety risks. The protected antibodies exhibit extraordinary thermal, chemical, and mechanical stabilities, and they can survive for long-term storage (>3 weeks) under severe temperature variation (4 ↔ 50 °C) at a fast ramp rate (25 °C min-1 ). More importantly, the encapsulated antibodies can be easily released as quickly as 10 s with high efficiency (≈100%) to completely remove the MOFs before use. This study paves a new avenue for the facile preparation and storage of biopharmaceuticals represented by antibodies under ambient or perturbation conditions, which may greatly broaden and promote the applications of both MOFs and biopharmaceuticals.

An auspicious combination: Fast-ramping battery energy storage and high-capacity pumped hydro

Pumped hydro represents the most mature energy storage technology and accounts for more than 99 % of bulk storage capacity worldwide. Nevertheless, energy storage is becoming today increasingly diversified. Battery costs have fallen massively the last years due to increased deployment and interest in storage for variable renewable energy integration. The most dramatic cost developments have been for Li-Ion chemistries, driven by the development and perspectives of the electric vehicle market. Existing or new build pumped-storage hydro power plants (PSP) provide potential for being extended by container-based battery energy storage systems (BESS) as the techno-organisational set-up can be commonly used. Apart from the technological infrastructure (high voltage installations with grid interface as well as the control, communication and monitoring systems), the required marketing and energy trading competences are available. Due to their very fast ramping capabilities, BESS are well suitable for the participation in the primary reserve (R1) market. Compared to secondary (R2) and minutes reserves (R3) markets, the R1 market promises the largest benefits for any kind of storage. By pooling of PSP and BESS, the control aggregate can make use of the advantages of the two individual technologies: the fast ramping capability of BESS and the large autonomy of PSP. In the paper, the authors discuss different modes of aggregation of PSP and BESS for their joint participation in the R1 market. Therefore, boundary conditions of possible operation on the R1 market defined by TSOs are laid down and their implications on the PSP-battery aggregate are presented. The authors show, how an aggregation of PSP and BESS can operate. Herein, the objective is to maximise the marketable reserve capacity. The contribution is based on the implementation and commissioning experience of a 12.5 MW / 13 MWh Li-Ion BESS, which enhances the reserve capacity of the existing Pfreimd hydro power plant group in Germany.

Synthesis of N-doped mesoporous TiO2 by facile one-step solvothermal process for visible light photocatalytic degradation of organic pollutant

Utilization of visible-light in photocatalysis is one of the key aspects of achieving effective application. Non-metal doping solely is often not adequate to give a genuinely practical solution because of challenging separation process. Here, we demonstrate the facile synthesis of modified TiO2 by non-metal N-doping and surface modification through a one-step solvothermal method. Under this process, both N-dopant and CTAB could be introduced in one process thus creating N-doped mesoporous TiO2 after template removal using calcination. N2 physisorption indicated high specific surface area up to 148.60 m2/g. Furthermore, the adsorption-desorption isotherm curve exhibited type IV thus confirming the presence of a mesoporous structure, with H1 and H2 hysteresis loop for slow and fast ramp calcination, respectively. Various characterizations were also carried out to explain the possible band-gap reduction mechanism which leads to the workability extension of the as-synthesized photocatalyst. Faster and superior settling capability was shown qualitatively using static settling test. The performance of the modified photocatalysts showed improved performance in methylene blue (cationic dye) and methyl orange (anionic dye) degradation under visible light (λ > 400 nm) as compared to other commercially available TiO2 photocatalysts. In conclusion, facile modifications introduced in this research proved to bring constructive effect, establishing better photocatalyst with effective utilization of visible light and also simple to retrieve catalyst.

(Invited) Advanced CMOS Scaling: Challenges, Metrology and Characterization Needs

Over the past decade, CMOS device and integrated circuit technology has rapidly evolved toward the use of complex 3D structures that are fabricated using new materials and processes with ever decreasing dimensions. FinFET transistor is now the dominant microprocessor device architecture, and the challenges associated with its 3D nature of all measurements are amplified by shrinking dimensions. This paper reviews the device physics and key front end wafer fabrication challenges of the state-of-the-art FinFET technology. It highlights the area of metrology and characterization that is needed to enable process development, fast ramping in pilot lines and start-ups, reducing time-to-market for new products and yield improvement in mature factories

Composition and Strain Evolution of Undoped Si0.8Ge0.2 Layers Submitted to UV-Nanosecond Laser Annealing

For CMOS scaling beyond 10 nm technology node, high active dopant concentrations in sources and drains are required to minimize contact resistance. Given its ability to reach high temperatures with extremely fast ramps, pulsed laser annealing is used in PMOS and NMOS transistors fabrication to obtain highly doped SiGe:B [1] and Si:P [2] regions. However, there are still few studies on the impact of nanosecond laser annealing on SiGe. We have thus investigated the behavior of thin, pseudomorphic Si0.8Ge0.2 layers submitted to ultraviolet nanosecond laser annealing in a wide range of laser energy densities. Undoped, 30 nm thick pseudomorphic Si0.8Ge0.2 layers were grown at 550°C on (100) Si substrates in a Reduced Pressure CVD reactor. They were subsequently laser annealed in a SCREEN LT-3100 platform operating at 308 nm with a 160 ns pulse duration. The laser energy density was increased from 1.40 up to 2.40 J/cm² in order to investigate various regimes, from SiGe layer sub-melt to a point at which the whole SiGe layer and part of the Si substrate reach the melt. Time Resolved Reflectometry (TRR) and SP2 haze measurements combined with Atomic Force Microscopy (AFM) were used to detect melt threshold and quantify surface roughness evolutions, respectively. High Resolution X-Ray Diffraction and Time-Of-Flight-Secondary Ions Mass Spectrometry characterizations were performed to assess layer composition, strain and crystalline quality as a function of the laser energy density. Melt threshold was detected at 1.55 J/cm² with SP2 Haze measurements (Fig.2) and at 1.58 J/cm² by TRR (Fig. 1). When increasing the laser energy density, three different regimes were identified. In the sub-melt regime, i.e. at energy densities lower than 1.55 J/cm², the annealed samples showed neither surface nor volume differences compared to the as-grown sample. For higher energy densities, part of the Si0.8Ge0.2 layer melted. At first, the melt remained very shallow: TOF-SIMS at 1.59 J/cm² (Fig.3) and Reciprocal Space Map (RSM, not shown here) were identical to those for the reference sample. However, a strong increase in haze and roughness indicated that the surface was modified. For a deeper melt (annealing at 1.8 J/cm²), the germanium was redistributed over the melted depth and segregated towards the surface, creating a top layer with a higher germanium concentration (cf. Fig.3). The solidification and segregation were accompanied by a partial relaxation of the layer up to 25% (the SiGe layer peak in Fig. 4.b is broadened due to mosaicity and not at the same Qx coordinate than that of the Si substrate) while the surface stayed rough. At higher energy density values, for instance 2.0 J/cm² (still in the partial melt regime), germanium segregation still occured and resulted in an even higher germanium concentration near the surface, up to 40%. However, the quality of the layer strongly improved compared to that of the 1.8 J/cm² sample. Roughness and haze were indeed much lower and close to their initial level. The RSM in Fig.4.c indicates that the layer is pseudomorphic, with a rather good crystalline quality, which will be further assessed by TEM observations. This sub-regime with strained SiGe layers exhibiting a high concentration of germanium near the surface could be favorable to the formation of low-resistance contacts in in-situ doped layers [2]. For higher energy densities, the whole SiGe layer and part of the Si substrate were melted: we were then in the full melt regime. For an annealing at 2.4 J/cm², the deeper melt and the intermixing resulted in the formation of a pseudomorphic 85 nm-thick Si0.93 Ge0.07 layer, with an almost uniform germanium profile. The film seems to have a very good crystalline quality as seen in Fig.4.d while RSM, Roughness and haze values were similar to those of the as-grown sample. It is therefore possible, by selecting the appropriate energy densities, to form pseudomorphic SiGe layers with a high germanium content near the surface, which would be favorable for electrical contact formation. Among all the annealing regimes, it seems to be the most promising one for further investigations with doped layers.

Effect of temperature ramp rate during the primary drying process on the properties of amorphous-based lyophilized cake, Part 2: Successful lyophilization by adopting a fast ramp rate during primary drying in protein formulations

In the lyophilization process for injections, the shelf temperature (Ts) and chamber pressure (Pc) have mainly been investigated to optimize the primary drying process. The objective of this study was to show that lyophilization of protein formulations can be achieved by adopting a fast ramp rate of Ts in the beginning of the primary drying process. Bovine serum albumin was used as the model protein, and seven different lyophilized formulations obtained were stored at elevated temperature. We found that although acceptable cake appearance was confirmed by the fast ramp cycle, all formulations of lyophilized cakes obtained by the slow ramp cycle severely collapsed (macrocollapse). It is thought that the collapse in the slow ramp cycle occurred during the shelf ramp in the beginning of primary drying and that insufficient removal of water from the dried matrix caused viscous flow (product collapse). Regarding storage stability, moisture-induced degradation was confirmed in some of the formulations prepared by the slow ramp cycle, whereas all lyophilized BSA formulations prepared by the fast ramp cycle were stable. Thus, the results indicate that the ramp rate appears to be one of the critical operational parameters required to establish a successful lyophilization cycle.

Incoming and Inline Defectivity Control Solutions for Silicon Carbide Manufacturing

Si l icon car b ide (Si C ) man u f act u ring is transitioning from 4 inch wafers to 6 inch wafers for production line devices. The main obstacle for SiC manufacturing high yield is defect control. Defectiveness inline control is well established for silicon power device. However, there are two main challenges related to SiC technology. The first challenge is incoming 4H-SiC substrates defectivity and epi layer crystallographic defects. The second challenge is inline defect detection at process steps such as implantation and annealing activation [,]. Defect detection and classification are difficult with current defect inspection tools because of substrate transparency at visible light, color variation, roughness, and wafers’ high warpage. In addition, SiC device integration has been requesting specific optimization. In this paper, collaboration studies have been done to develop solutions to these challenges. Yield correlation analyses have validated the process control flow set to address these two major challenges and to enable the fast ramp of the 6” production line of SiC devices.

Modeling cell-substrate de-adhesion dynamics under fluid shear

Changes in cell-substrate adhesion are believed to signal the onset of cancer metastasis, but such changes must be quantified against background levels of intrinsic heterogeneity between cells. Variations in cell-substrate adhesion strengths can be probed through biophysical measurements of cell detachment from substrates upon the application of an external force. Here, we investigate, theoretically and experimentally, the detachment of cells adhered to substrates when these cells are subjected to fluid shear. We present a theoretical framework within which we calculate the fraction of detached cells as a function of shear stress for fast ramps as well as the decay in this fraction at fixed shear stress as a function of time. Using HEK and 3T3 fibroblast cells as experimental model systems, we extract characteristic force scales for cell adhesion as well as characteristic detachment times. We estimate force-scales of ∼500 pN associated to a single focal contact, and characteristic time-scales of s representing cell-spread-area dependent mean first passage times to the detached state at intermediate values of the shear stress. Variations in adhesion across cell types are especially prominent when cell detachment is probed by applying a time-varying shear stress. These methods can be applied to characterizing changes in cell adhesion in a variety of contexts, including metastasis.

High-Temperature Molten Alkaline Water Electrolysis

The rapid development and deployment of fuel cell vehicles require large numbers of hydrogen (H2) refueling stations. Hydrogen production for mobile and energy storage applications from water electrolysis is attractive due to its high efficiency, fast ramp rates, and high-pressure capability. However, current hydrogen production from electrolysis comprises only a small fraction of the global hydrogen market due to the high cost associated with expensive stack materials (membrane, catalyst, and bipolar plates) and electricity consumption of the commercially available electrolysis systems [1]. There are currently two main types of electrolyzers, both operating at moderate temperatures (50–80 ˚C): proton exchange membrane (PEM) and anion exchange membrane (AEM). Alkaline membrane electrolyzer is a promising technology it suffers from poor AEM stability, particularly at elevated temperature (> 80 ℃). Giner has developed a high-temperature alkaline water electrolysis, molten alkaline electrolyte (MAE). In this technology, the high-temperature molten alkaline electrolyte employs lithium, sodium, or potassium hydroxide impregnated into a porous alumina or zirconia matrix as the electrolyte membrane [2, 3]. The operating temperature can vary from 200 to 550 °C, depending on the category and ratio of individual electrolyte. In this work, we will present detailed configuration of high-temperature alkaline water electrolysis focusing on the alkaline composite electrolyte and non-precious metal electrodes, e.g., hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts using a single cell electrolyzer set-up. We have developed a component assembly process utilizing a tape-casting method and a unique facility has been designed and constructed. The OH– ion conductivity of single or binary hydroxide has been investigated, at a temperature between 300 to 550 °C. The temperature dependencies of conductivity for palletized composite single/binary hydroxide electrolyte are depicted in Figure 1. The binary hydroxide conductivity (LiOH-NaOH-melt-50) was higher compared to the single hydroxide (LiOH-50). The single or binary hydroxides went through premelting process before testing. This process was conducted to limit the evaporation, and the eventual loss, of the electrolyte during the testing by allowing the electrolyte to evaporate before testing began and not affect measurements and calculations conducted during testing. Design of experimental techniques have also been applied to optimize the ceramic membrane properties and to select non-precious HER/OER catalysts. The single cellperformance using selected molten alkaline electrolyte will also be discussed. Figure 1 Temperature-dependence of OH– ion conductivity of composite single/binary hydroxide electrolyte at a temperature between 300 °C to 550 °C. References Anthony, J. Rand, and R. Dell, Hydrogen Energy Challenges and Prospects (RSC Energy Series) DOI: 10.1039/9781847558022 (2008).Huang, C. Yuh, US Patent 5,869,203 (1999).Patil, S. Yoon, J. Han, T. Lim, S. Nam, I. Oh, Int. J. Hydrogen Energy, 36, 6237-6247 (2011). Figure 1

Reliability and Physiological Interpretation of Pulmonary Gas Exchange by "Circulatory Equivalents" in Chronic Heart Failure.

BackgroundPeak ratios of pulmonary gas‐exchange to ventilation during exercise (V˙O2/V˙E and V˙CO2/V˙E, termed “circulatory equivalents”) are sensitive to heart failure (HF) severity, likely reflecting low and/or poorly distributed pulmonary perfusion. We tested whether peak V˙O2/V˙E and V˙CO2/V˙E would: (1) distinguish HF patients from controls; (2) be independent of incremental exercise protocol; and (3) correlate with lactate threshold (LT) and ventilatory compensation point (VCP), respectively.Methods and ResultsTwenty‐four HF patients (61±11 years) with reduced ejection fraction (31±8%) and 11 controls (63±7 years) performed ramp‐incremental cycle ergometry. Eighteen HF patients also performed slow (5±1 W/min), medium (9±4 W/min), and fast (19±6 W/min) ramps. Peak V˙O2/V˙E and V˙CO2/V˙E from X‐Y plot, and LT and VCP from 9‐panel plot, were determined by 2 independent, blinded, assessors. Peak V˙O2/V˙E (31.2±4.4 versus 41.8±4.8 mL/L; P<0.0001) and V˙CO2/V˙E (29.3±3.0 versus 36.9±4.0 mL/L; P<0.0001) were lower in HF than controls. Within individuals, there was no difference across 3 ramp rates in peak V˙O2/V˙E (P=0.62) or V˙CO2/V˙E (P=0.97). Coefficient of variation (CV) in peak V˙O2/V˙E was lower than for LT (5.1±2.1% versus 8.2±3.7%; P=0.014), and coefficient of variation in peak V˙CO2/V˙E was lower than for VCP (3.3±1.8% versus 8.7±4.2%; P<0.001). In all participants, peak V˙O2/V˙E was correlated with, but occurred earlier than, LT (r 2=0.94; mean bias, −0.11 L/min), and peak V˙CO2/V˙E was correlated with, but occurred earlier than, VCP (r 2=0.98; mean bias −0.08 L/min).ConclusionsPeak circulatory equivalents during exercise are strongly associated with (but not identical to) LT and VCP. Peak circulatory equivalents are reliable, objective, effort‐independent indices of gas‐exchange abnormality in HF.

Stress Introduction Rate Alters the Benefit of AcrAB-TolC Efflux Pumps.

Stress tolerance studies are typically conducted in an all-or-none fashion. However, in realistic settings-such as in clinical or metabolic engineering applications-cells may encounter stresses at different rates. Therefore, how cells tolerate stress may depend on its rate of appearance. To address this, we studied how the rate of stress introduction affects bacterial stress tolerance by focusing on a key stress response mechanism. Efflux pumps, such as AcrAB-TolC of Escherichia coli, are membrane transporters well known for the ability to export a wide variety of substrates, including antibiotics, signaling molecules, and biofuels. Although efflux pumps improve stress tolerance, pump overexpression can result in a substantial fitness cost to the cells. We hypothesized that the ideal pump expression level would involve a rate-dependent trade-off between the benefit of pumps and the cost of their expression. To test this, we evaluated the benefit of the AcrAB-TolC pump under different rates of stress introduction, including a step, a fast ramp, and a gradual ramp. Using two chemically diverse stresses, the antibiotic chloramphenicol and the jet biofuel precursor pinene, we assessed the benefit provided by the pumps. A mathematical model describing these effects predicted the benefit as a function of the rate of stress introduction. Our findings demonstrate that as the rate of introduction is lowered, stress response mechanisms provide a disproportionate benefit to pump-containing strains, allowing cells to survive beyond the original inhibitory concentrations.IMPORTANCE Efflux pumps are ubiquitous in nature and provide stress tolerance in the cells of species ranging from bacteria to mammals. Understanding how pumps provide tolerance has far-reaching implications for diverse fields, from medicine to biotechnology. Here, we investigated how the rate of stressor appearance impacts tolerance. We focused on two distinct substrates of AcrAB-TolC efflux pumps, the antibiotic chloramphenicol and the biofuel precursor pinene. Interestingly, tolerance is highly dependent on the rate of stress introduction. Therefore, it is important to consider not only the total quantity of a stressor but also the rate at which it is applied. The implications of this work are significant because environments are rarely static; antibiotic concentrations change during dosing, and metabolic engineering processes change with time.

Optimal Load-Side Control for Frequency Regulation in Smart Grids

Frequency control rebalances supply and demand while maintaining the network state within operational margins. It is implemented using fast ramping reserves that are expensive and wasteful, and which are expected to become increasingly necessary with the current acceleration of renewable penetration. The most promising solution to this problem is the use of demand response, i.e., load participation in frequency control. Yet it is still unclear how to efficiently integrate load participation without introducing instabilities and violating operational constraints. In this paper, we present a comprehensive load-side frequency control mechanism that can maintain the grid within operational constraints. In particular, our controllers can rebalance supply and demand after disturbances, restore the frequency to its nominal value, and preserve interarea power flows. Furthermore, our controllers are distributed (unlike the currently implemented frequency control), can allocate load updates optimally, and can maintain line flows within thermal limits. We prove that such a distributed load-side control is globally asymptotically stable and robust to unknown load parameters. We illustrate its effectiveness through simulations.

Iron-containing carbon molecular sieve membranes for advanced olefin/paraffin separations

In this work, carbon molecular sieve (CMS) dense film membranes derived from 6FDA-DAM:DABA (3:2) polyimide precursor were studied for separation of mixed olefins (C2H4 and C3H6) from paraffins (C2H6 and C3H8). Olefin-selective CMS membranes with high performance can be made by pyrolysis of metal-containing polymeric precursors. Pyrolyzed at 550°C with a fast ramp rate, CMS membranes with integrated Fe2+ (2.2wt% in the precursor) showed 19% higher C2H4/C2H6 and 11% higher C3H6/C3H8 sorption selectivity than that of the neat CMS membrane. Additional investigations with a quaternary mixture feed (C2 and C3 hydrocarbons) show that C2H4 permeability above 10 Barrers with C2H4/C2H6 permselectivity near 11 were achieved for the 3.2wt% Fe loading case. Although Fe incorporation did not appear to promote C3H6/C2H6 permselectivity, Fe is useful to improve C2 pair olefin/paraffin separation. Deconvolution of the C2H4/C2H6 permselectivity for our more extensively studied 2.2wt% loading case was also revealing. While both sorption and diffusion selectivity increased due to the Fe incorporation, a larger influence is seen on the diffusion selectivity versus the sorption selectivity. Hypotheses to explain this surprising outcome are offered to guide future work.

TTT‐diagram for epoxy film adhesives using quasi‐isothermal scans with initial fast ramps

ABSTRACTThe characterization of film adhesives is challenging because they required freezer storage, contain an inseparable filler—thermoplastic knit or fiber‐reinforcement, and are heat activated systems with a pre‐cure and unknown chemistry. A testing protocol that eliminates these sources of error is proposed. This study presents a method to generate time–temperature‐transformation (TTT) diagrams of epoxy film adhesives via differential scanning calorimetry (DSC). Non‐isothermal and isothermal DSC scans are used to capture the reaction and the glass transition temperature. The use of an initial fast ramp—up to 500 K/min—in the isothermal scans is explored for the first time. This technique shows the potential to produce a quasi‐isothermal cycle, eliminating the loss of data in the initial stage of the reaction. The total heat released, the activation energy, and the fractional kinetic parameter, are estimated via model‐free methods. The Kamal–Sourour model and the formal kinetic model are fit to model the rate of cure. The simplest model that accurately captures the reaction, a parallel two‐step model, A , is outlined. The glass transition temperature is modeled via DiBenedetto's equation to include the diffusion‐controlled mechanism. The TTT‐diagrams of two commercial adhesives, DA 408 and DA 409, are shown with an analysis of processing optimization. The use of quasi‐isothermal scans with initial fast ramps combined with the correction for filler, moisture, and pre‐curing history can be applied to characterize fast curing thermosets, complex B‐stage resins, and thermosetting composites. The modeling results can also be used in numerical studies of residual stresses and dimensional stability in the manufacturing of thermosetting composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45791.

Flexibility-Based Reserve Scheduling of Pumped Hydroelectric Energy Storage in Korea

The high penetration of renewable energy resources has made it harder to secure a flexible power system. Accordingly, this has become an issue in operating power systems. As a possible solution, pumped hydroelectric energy storage (PHES) has received much attention because of its fast start-up and ramp characteristics. This study proposes a flexibility-based reserve scheduling method for PHES. In this method, the reserve scheduling of PHES was conducted to improve flexibility; the associated risk index was termed the ramping capability shortage expectation (RSE). The peak-load days in 2016 and 2029 were selected to examine the applicability and performance of the proposed method. Results indicate that the proposed method can improve the flexibility by 4.45% for 2016 and 0.9% for 2029, respectively.

A New Energy-Saving Catalytic System: Carbon Dioxide Activation by a Metal/Carbon Catalyst.

The conversion of CO2 into useful chemicals is an attractive method to reduce greenhouse gas emissions and to produce sustainable chemicals. However, the thermodynamic stability of CO2 means that a lot of energy is required for its conversion into chemicals. Here, we suggest a new catalytic system with an alternative heating system that allows minimal energy consumption during CO2 conversion. In this system, electrical energy is transferred as heat energy to the carbon-supported metal catalyst. Fast ramping rates allow high operating temperatures (Tapp =250 °C) to be reached within 5 min, which leads to an 80-fold decrease of energy consumption in methane reforming using CO2 (DRM). In addition, the consumed energy normalized by time during the DRM reaction in this current-assisted catalysis is sixfold lower (11.0 kJ min-1 ) than that in conventional heating systems (68.4 kJ min-1 ).

(Invited) A Hybrid CMOS-Graphene Integrated Sensing Platform for Subsecond Dopamine Detection

Understanding dopamine signaling in the brain has important scientific and clinical implications. However, a standard tool that is capable of measuring dopamine with high spatiotemporal resolution is currently unavailable. Here, we present a new integrated sensing platform for subsecond detection of dopamine by combining advanced silicon CMOS and graphene nanotechnology. We demonstrate the functionality of our heterogeneous integrated sensors through in vitro measurements. This integrated sensing technology makes the foundation for realizing neural probes that are capable of measuring dopamine concurrently in multiple locations in the brain with high temporal resolution. Fast-scan cyclic voltammetry (FSCV) using carbon fiber electrodes has proven to be a reliable method for in vivo detection of phasic dopamine signal. The FSCV measurement produces two overlapping current signals: (i) a large non-informative background current due to the charge and the discharge of the double layer capacitance, and (ii) a small faradaic signal due to the redox reactions of dopamine molecules. In FSCV, applying a fast voltage ramp increases the sensitivity and the temporal resolution. However, the non-informative background current also becomes larger at faster ramp rates, thereby making the detection of the small faradaic signal more difficult. Furthermore, the environmental noise is a limiting factor for the detection of dopamine at the physiological levels of interest, particularly in animals with large brains. Finally, the large cylindrical shape of carbon fiber electrodes complicates the development of multielectrode arrays, necessary for large-scale measurements of dopamine concentration. To address these technical challenges, we combine advances in nanofabrication with silicon chip manufacturing and create a heterogeneous integrated CMOS-graphene sensing platform that would enable accurate measurements of dopamine with high spatiotemporal resolution. To accurately measure the small faradaic current, we developed an integrated readout circuit using a standard 65nm process. Leveraging the high specificity of FSCV, the readout chip is configured to capture the signal of interest at about the redox potentials. Also, a fixed low-noise current continuously subtracts a large portion of the non-informative background current near the redox potentials, while maintaining the overall shape of the signal. Our readout approach, therefore, makes the CMOS chip compact and power-efficient. We replaced carbon fiber with a few-layer graphene film because the thin planar structure of graphene facilitates the fabrication of a multielectrode array. Furthermore, significant advances in large-area synthesis of graphene using chemical vapor deposition offer a manufacturable solution for large-scale deployment of this integrated sensing technology. These features enabled the direct integration of graphene sensor arrays on top of the CMOS readout chip. We validated the performance of our integrated sensing platform through in vitro measurements. In conclusion, we introduced and implemented a heterogeneous integrated CMOS-graphene sensor for measuring dopamine concentration using fast-scan cyclic voltammetry. Our core sensing technology offers a new pathway for developing the next generation of neural probes that can accurately monitor dopamine signaling with high spatiotemporal resolution in the brain.

Quasi‐isothermal DSC testing of epoxy adhesives using initial fast heating rates

ABSTRACTThree major factors decrease the accuracy of the cure measurement in standard‐isothermal testing using differential scanning calorimetry (DSC). First, cure occurs during the heating step. Second, data are lost during the stabilization period between the dynamic and isothermal step. Third, the baseline selection requires a modification to the protocol. An alternative, which is explored in this study, is the use of fast ramps, which decrease the heating time, but this has been avoided due to overshoot that occurs between the dynamic and isothermal step, which is troublesome for systems with autocatalytic kinetics. By mitigating these factors, a quasi‐isothermal protocol was developed. Therefore, more complete cure kinetics were captured with the implementation of fast DSC to decrease the ramp time and through the optimization of furnace parameters to decrease stabilization time and temperature overshoot. The data suggested this quasi‐isothermal analysis more accurately measured the isothermal curing kinetics of a commercial epoxy adhesive at 110, 115, and 120 °C for fast ramps of 175, 350, and 500 K/min compared to the traditional ramp of 5 K/min. The enthalpy spike at the dynamic to isothermal transition remains an issue; however, an empirical shift can be used to compensate for the enthalpy signal lag. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45425.

Computational Analysis of Dynamic Tubular SOFC with a Built-in Chemical Iron Bed

Solid oxide fuel cells (SOFCs) with enhanced fast ramping power capability and overload tolerance can find important applications in grid frequency regulation and data center overload protection. Recently, we have demonstrated a new SOFC configuration featuring a built-in chemical Fe-bed in the anode chamber of a tubular SOFC and exceptional fast power ramping and overload tolerance. In this presentation, we showed our theoretical understanding of the enhanced dynamic performance through a two-dimensional axial symmetrical numerical model. The model couples the charge and mass transport in the tubular SOFC with chemical reaction kinetics in the Fe-bed, producing axial distributions of Nernst potential, H2O/H2 molar ratio, local current density and fuel utilization under different operating conditions. The crucial role of Fe-bed in providing instant fuel to support fast ramping and overload currents has been explicitly explained by this computational model.

Effects of amplitude and predictability of perturbations to the arm on anticipatory and reactionary muscle responses to maintain balance

Disturbances to balance arising from forces applied to the upper limb have received relatively little attention compared to disturbances arising from support surface perturbations. In this study we applied fast ramp perturbations to the hand in anterior, posterior, medial and lateral directions. The effects of perturbation predictability and amplitude on the postural response of upper limb, trunk and lower limb muscles were investigated. Perturbations were applied either in blocks of constant amplitude and direction (predictable) or with direction and amplitude varying randomly (random) from trial to trial. The spatial-temporal patterns of anticipatory muscle activation under the predictable condition and the reactionary responses following the perturbation under both conditions were similarly organized. The size of the response increased systematically with the perturbation magnitude for both anticipatory and reactionary changes in muscle activation. However, the slope of the relation between perturbation amplitude and the magnitude of the change in muscle activation was greater when perturbations were predictable than when they were randomly selected. The timing of both the anticipatory and reactionary increases in muscle activation was invariant across perturbation amplitudes. The characteristics of the reactionary responses have a similar organization to the long latency muscle responses to support surface perturbations.