Step Transition Research Articles

Numerical study on shape functions for optimal exploitation of the acoustic black hole effect

AbstractThe acoustic black hole (ABH) effect offers a great possibility to damp a whole construction in a very efficient way. The main idea of this approach is to weaken thin structures locally to concentrate the structure‐borne sound energy in this area. Therefor material is removed in a certain region, which is referred to as an ABH. This measure leads to a focusing of acoustically critical bending waves. By applying a damping measure, e.g. constraint‐layer damping, within the ABH, the structure is globally damped by a local measure.The shape function of an ABH is a major issue for optimizing the efficiency of damping. The material diminution, equivalent to the reduction of the mechanical impedance, has to be smooth in order to avoid reflection of bending waves. In literature, a power function with a higher order than two is recommended. Focusing the structure‐borne sound works better by increasing the order. The limit case is infinite order which is a sharp step transition. This is equivalent to an impedance step which is well known to lead to a high portion of reflection and therefor reducing the efficiency of the ABH area. There must be an optimum between these two limits, quadratic and infinite order, in an acoustical sense.In this paper, numerical studies are carried out to determine the optimal order for a power function approach as shape function of an ABH. For this purpose, a beam is used as a generic structure. In addition, alternative function approaches are investigated and compared.

Two-Dimensional Symmetric Box Delivery Motion Prediction and Validation: Subtask-Based Optimization Method

Box delivery is a complicated manual material handling task which needs to consider the box weight, delivering speed, stability, and location. This paper presents a subtask-based inverse dynamic optimization formulation for determining the two-dimensional (2D) symmetric optimal box delivery motion. For the subtask-based formulation, the delivery task is divided into five subtasks: lifting, the first transition step, carrying, the second transition step, and unloading. To render a complete delivering task, each subtask is formulated as a separate optimization problem with appropriate boundary conditions. For carrying and lifting subtasks, the cost function is the sum of joint torque squared. In contrast, for transition subtasks, the cost function is the combination of joint discomfort and joint torque squared. Joint angle profiles are validated through experimental results using Pearson’s correlation coefficient (r) and root-mean-square-error (RMSE). Results show that the subtask-based approach is computationally efficient for complex box delivery motion simulation. This research outcome provides a practical guidance to prevent injury risks in joint torque space for workers who deliver heavy objects in their daily jobs.

Temperature dependence of adsorption hysteresis in flexible metal organic frameworks

“Breathing” and “gating” are striking phenomena exhibited by flexible metal-organic frameworks (MOFs) in which their pore structures transform upon external stimuli. These effects are often associated with eminent steps and hysteresis in sorption isotherms. Despite significant mechanistic studies, the accurate description of stepped isotherms and hysteresis remains a barrier to the promised applications of flexible MOFs in molecular sieving, storage and sensing. Here, we investigate the temperature dependence of structural transformations in three flexible MOFs and present a new isotherm model to consistently analyse the transition pressures and step widths. The transition pressure reduces exponentially with decreasing temperature as does the degree of hysteresis (c.f. capillary condensation). The MOF structural transition enthalpies range from +6 to +31 kJ·mol−1 revealing that the adsorption-triggered transition is entropically driven. Pressure swing adsorption process simulations based on flexible MOFs that utilise the model reveal how isotherm hysteresis can affect separation performance.

Deep random walk of unitary invariance for large-scale data representation

Data representation aims at learning an efficient low-dimensional representation, which is always a challenging task in machine learning and computer vision. It can largely improve the performance of specific learning tasks. Unsupervised methods are extensively applied to data representation, which considers the internal connection among data. Most of existing unsupervised models usually use a specific norm to favor certain distributions of the input data, leading to an unsustainable encouraging performance for given learning tasks. In this paper, we propose an efficient data representation method to address large-scale feature representation problems, where the deep random walk of unitary invariance is exploited for learning discriminative features. First, the data representation is formulated as deep random walk problems, where unitarily invariant norms are employed to capture diverse beneficial perspectives hidden in the data. It is embedded into a state transition matrix model, where an arbitrary number of transition steps is available for an accurate affinity evaluation. Second, data representation problems are then transformed as high-order matrix factorization tasks with unitary invariance. Third, a closed-form solution is proved for the formulated data representation problem, which may provide a new perspective for solving high-order matrix factorization problems. Finally, extensive comparative experiments are conducted in publicly available real-world data sets. In addition, experimental results demonstrate that the proposed method achieves better performance than other compared state-of-the-art approaches in terms of data clustering.

The impact of continuous quality improvement on coverage of antenatal HIV care tests in rural South Africa: Results of a stepped-wedge cluster-randomised controlled implementation trial.

Evidence for the effectiveness of continuous quality improvement (CQI) in resource-poor settings is very limited. We aimed to establish the effects of CQI on quality of antenatal HIV care in primary care clinics in rural South Africa. We conducted a stepped-wedge cluster-randomised controlled trial (RCT) comparing CQI to usual standard of antenatal care (ANC) in 7 nurse-led, public-sector primary care clinics-combined into 6 clusters-over 8 steps and 19 months. Clusters randomly switched from comparator to intervention on pre-specified dates until all had rolled over to the CQI intervention. Investigators and clusters were blinded to randomisation until 2 weeks prior to each step. The intervention was delivered by trained CQI mentors and included standard CQI tools (process maps, fishbone diagrams, run charts, Plan-Do-Study-Act [PDSA] cycles, and action learning sessions). CQI mentors worked with health workers, including nurses and HIV lay counsellors. The mentors used the standard CQI tools flexibly, tailored to local clinic needs. Health workers were the direct recipients of the intervention, whereas the ultimate beneficiaries were pregnant women attending ANC. Our 2 registered primary endpoints were viral load (VL) monitoring (which is critical for elimination of mother-to-child transmission of HIV [eMTCT] and the health of pregnant women living with HIV) and repeat HIV testing (which is necessary to identify and treat women who seroconvert during pregnancy). All pregnant women who attended their first antenatal visit at one of the 7 study clinics and were ≥18 years old at delivery were eligible for endpoint assessment. We performed intention-to-treat (ITT) analyses using modified Poisson generalised linear mixed effects models. We estimated effect sizes with time-step fixed effects and clinic random effects (Model 1). In separate models, we added a nested random clinic-time step interaction term (Model 2) or individual random effects (Model 3). Between 15 July 2015 and 30 January 2017, 2,160 participants with 13,212 ANC visits (intervention n = 6,877, control n = 6,335) were eligible for ITT analysis. No adverse events were reported. Median age at first booking was 25 years (interquartile range [IQR] 21 to 30), and median parity was 1 (IQR 0 to 2). HIV prevalence was 47% (95% CI 42% to 53%). In Model 1, CQI significantly increased VL monitoring (relative risk [RR] 1.38, 95% CI 1.21 to 1.57, p < 0.001) but did not improve repeat HIV testing (RR 1.00, 95% CI 0.88 to 1.13, p = 0.958). These results remained essentially the same in both Model 2 and Model 3. Limitations of our study include that we did not establish impact beyond the duration of the relatively short study period of 19 months, and that transition steps may have been too short to achieve the full potential impact of the CQI intervention. We found that CQI can be effective at increasing quality of primary care in rural Africa. Policy makers should consider CQI as a routine intervention to boost quality of primary care in rural African communities. Implementation research should accompany future CQI use to elucidate mechanisms of action and to identify factors supporting long-term success. This trial is registered at ClinicalTrials.gov under registration number NCT02626351.

Yapım Firmalarının Kurumsal Risk Yönetimi Olgunluğunda Risk Yöneticisinin Rolü

Addressing the risk management process with a holistic approach, enterprise risk management (ERM) enables efficient business processes to be carried out. Achieving success in time, cost and quality factors for complex projects in the constantly evolving construction industry requires systematic and holistic management approaches. In the management process of the construction projects, managing the possible risks from a holistic perspective is critical to the success and efficiency of the construction projects. However, in the companies operating in the construction sector, the transition steps from project-level risk management to corporate risk management have just begun and the level of maturity has not yet been reached. In this context, the main purpose of this study is to reveal the effect of the existence of the risk manager and corporate risk managament structuring on the corporate risk management maturity level of the construction companies. For this purpose, six main factors (stability of the board and senior management, having corporate risk management, risk identification, analysis and response, integrating corporate risk management into business processes, setting targets, and sufficient resources) are obtained as a result of a comprehensive literature review and a survey field study was organized. The data were analyzed with descriptive statistics and ANOVA analysis methods. As a result of the study carried out, the effect of the presence of the risk manager on the maturity level of corporate risk management in the construction companies and the impact and importance levels of the basic factors on the maturity of ERM were determined and compared. This study shed light on future studies to be done by examining the conceptual framework regarding ERM maturity levels in production companies.

Microclimatic Effects of a Forest-to-Peatland Transition on Aerodynamic Resistance to Water Vapour Transfer in the Sub-humid Boreal Plains

Peatlands often experience turbulent sheltering from their surrounding upland forests, which results in spatially variable surface–atmosphere exchanges of momentum, heat, and moisture produced by flow-separation dynamics, which suppresses the transport of such scalars in the sheltered region while promoting transport in the reattachment zone. With evapotranspiration being the dominant source of water loss in the Boreal Plains, it is necessary to understand the dynamics and controls on evapotranspiration within these peatlands. We used the regional atmospheric forest large-eddy simulation (RAFLES) model to study the impact of flow separation and surface roughness on microclimates leeward of a forest-to-peatland roughness transition. We parametrized our simulation with observed vegetation characteristics and meteorological data from three natural peatlands to accurately estimate natural ranges of peatland roughnesses and energy dynamics. Our simulations show that changes to peatland roughness do not affect the distances required for flow reattachment, and therefore the size of the sheltered region. However, increasing the surface roughness produces greater surface turbulence, quicker flow recovery, and decreased flow reversals within the sheltered region. Further, substantial microclimatic differences are observed throughout the flow regions of the roughness transition. Our results show that turbulence, aerodynamic resistance, and the microclimate vary throughout the backward-facing step transition and should be taken into account when estimating the spatial dynamics of evaporative demand leeward of a roughness transition. Furthermore, increasing the surface roughness of a peatland minimizes the spatial variability of turbulent drivers of evapotranspiration across a roughness transition. That is, flow separation and the surface roughness of the peatland should be accounted for when estimating the spatial variability and total evaporative potential across a peatland.

A scalable and reproducible manufacturing process for Phlebotomus papatasi salivary protein PpSP15, a vaccine candidate for leishmaniasis

Cutaneous leishmaniasis is a parasitic and neglected tropical disease transmitted by the bites of sandflies. The emergence of cutaneous leishmaniasis in areas of war, conflict, political instability, and climate change has prompted efforts to develop a preventive vaccine. One vaccine candidate antigen is PpSP15, a 15 kDa salivary antigen from the sandfly Phlebotomus papatasi that facilitates the infection of the Leishmania parasite and has been shown to induce parasite-specific cell-mediated immunity. Previously, we developed a fermentation process for producing recombinant PpSP15 in Pichia pastoris and a two-chromatographic-step purification process at 100 mL scale. Here we expand the process design to the 10 L scale and examine its reproducibility by performing three identical process runs, an essential transition step towards technology transfer for pilot manufacture. The process was able to reproducibly recover 81% of PpSP15 recombinant protein with a yield of 0.75 g/L of fermentation supernatant, a purity level of 97% and with low variance among runs. Additionally, a freeze-thaw stability study indicated that the PpSP15 recombinant protein remains stable after undergoing three freeze-thaw cycles, and an accelerated stability study confirmed its stability at 37 °C for at least one month. A research cell bank for the expression of PpSP15 was generated and fully characterized. Collectively, the cell bank and the production process are ready for technology transfer for future cGMP pilot manufacturing.

Bull’s-Eye Antenna With Circular Polarization at Millimeter Waves Based on Ridge Gap Waveguide Technology

In this communication, a Bull's-Eye (BE) antenna with circular polarization (CP) based on ridge gap waveguide (RGW) technology is numerically and experimentally demonstrated. The structure is excited from the bottom with a standard WR-15 waveguide ( V-band) coupled through a step transition to a ridgeline that ends in two orthogonal arms of different lengths to generate CP. Radiation is coupled to the top plate by a central diamond slot surrounded by the BE structure, which consists of four concentric periodic corrugations around the slot. Simulations and experimental results are in good agreement, with axial ratio below 1 dB at the operation frequency and peak gain of 18.4 dB. The antenna has right-handed CP (RHCP) with polarization discrimination of more than 30 dB.

Greening states and societies: from transitions to great transformations

ABSTRACT This article examines the limits and potential of the state in orchestrating sustainability transitions from the standpoint of critical theory on the green state. Two interrelated questions are posed. First, to what extent are democratic capitalist states necessarily compromised in their functional capacity to orchestrate ecological sustainability? Second, in light of this analysis, how can a theory of the green state that claims to be critical and transformative, rather than merely problem-solving, provide practical guidance to state and societal change agents in approaching the political challenges of ecological transition? A critical method for approaching these challenges is outlined, encompassing conjunctural analysis followed by situated, critical problem solving, which is geared to identifying the ‘next best transition steps’ with the greatest long-term transformational potential. The method is briefly illustrated in relation to the critical conjuncture presented by the coronavirus pandemic.

Phase Transformation of Doped LiCoPO4 during Galvanostatic Cycling.

In situ X-ray diffraction was employed to investigate the crystal structure changes in Cr/Si co-doped Li(Co,Fe)PO4 cathode material during a galvanostatic charge/discharge process at a slow rate of C/30. The evolution of the X-ray patterns revealed that the phase transformation between the Cr/Si-Li(Co,Fe)PO4 and Cr/Si-(Co,Fe)PO4 is a two-step process, which involves the formation of an intermediate compound of Cr/Si-Li0.62(Co,Fe)PO4 upon the extraction of Li ions from the pristine phase. Different from the previously reported two biphasic transition steps, the phase transformation of the Cr/Si-Li(Co,Fe)PO4 followed a solid solution and a biphasic reaction pathway at different stages of the delithiation/lithiation process, respectively.

Implications of United States Medical Licensing Examination Step 1 Becoming Pass/Fail on the Integrated Plastic Surgery Match.

There has been much conversation surrounding the United States Medical Licensing Examination’s recent decision to transition Step 1 score reporting from a three-digit numeric score to a pass/fail outcome.1 Integrated plastic surgery is one of the most competitive matches for medical students.2 To be successful in the plastic surgery match, applicants must have strong board scores, extensive research experience, and numerous volunteer opportunities.2,3 Historically, Step 1 scores have provided an estimate for competitiveness for students.4 This change in scoring will effectively remove this means for self-selection. With a pass/fail system, students will have one less component with which to differentiate themselves from their peers. This may generate disadvantages to students attending U.S. medical schools outside of the top 40 in National Institutes of Health funding who previously had the opportunity to demonstrate their academic potential with an achievement-based standardized examination. With no numeric score for Step 1, naturally programs will have to seek other ways to differentiate students. At this point, Step 2 Clinical Knowledge will remain a numeric score, and consequently programs may use this to replace the importance of Step 1. However, Step 2 Clinical Knowledge is usually taken after the completion of the third year of medical school. Given the time delay for grading national board examinations, many students may not receive their scores until just before applications are due, which could leave students without enough time to estimate their competitiveness. Currently, many students delay taking Step 2 Clinical Knowledge until after applications are submitted to complete several away rotations as is expected in this specialty. Subsequently, the timing of these rotations could also be affected. The United States Medical Licensing Examination upholds that, across specialties, Step 1 scores positively correlate with specialty board pass rates.1 This is important for programs to consider, as board pass rates can have an impact on accreditation and program reputation. With the absence of Step 1 scores, programs may choose to put more weight into research experiences and productivity. Many students currently elect to take a year or more of dedicated research time within medical school.5 If programs were to place a higher emphasis on research, students completing their medical education in 4 years with no time off would be at an inherent disadvantage, not given the opportunity to equalize their applications with a strong performance on Step 1. A new form of applicant self-selection may occur based on research experience, similar to what has occurred in Canada after the implementation of a pass/fail scoring system.4 Similarly, without the standardized comparison of applicants provided by a uniform examination, equal comparisons of students between medical schools will be more difficult to achieve. This may lead to significant disadvantage for students coming from medical schools deemed to be less prestigious and limit these students’ opportunity for upward mobility. Although the termination of numeric Step 1 scores is a recent decision, it is important for programs to be proactive when considering factors for assessing future applicants and the effects that this change may have on the applicant pool at large. DISCLOSURE Neither of the authors has a financial interest to declare in relation to the content of this article. No funding was received for this work.

Understanding of multiple resistance states by current sweeping in MoS2-based non-volatile memory devices

Recently, various two-dimensional materials have been reported to exhibit non-volatile resistance switching phenomenon. The atomristors, featuring memristor effect in atomically thin nanomaterials such as monolayer transition metal dichalcogenides and hexagonal boron nitride, have drawn much attention due to the extremely thin active layer thickness with the advantages of forming-free characteristic, large on/off resistance ratio and fast switching speed. To investigate the switching mechanisms in the 2D monolayers, we introduced an electrical characterization method by current sweeping to illustrate the detailed information hidden in the commonly used voltage-sweep curves. Multiple transition steps have been observed in the SET process of MoS2-based resistance switching devices. The different behaviors of transition steps were attributed to the number of defects or vacancies associated with the switching phenomenon, which is consistent with the previously reported conductive-bridge-like model for 2D atomristors. This work provides an approach using current sweeping to precisely characterize the resistance switching effect and inspires further research to optimize the defect distribution in 2D materials for the applications in multi-bit non-volatile memory and neuromorphic computing.

Abstract 1521: New roles of ATP in metastasis: Extracellular and macropinocytosis internalized ATP work together to induces epithelial to mesenchymal transition and other early steps of metastasis

Abstract Metastasis is estimated to be responsible for more than 90% of all cancer-related deaths. Metastasis is initiated by induction of epithelial-mesenchymal transition (EMT) of cancer cells, but factors and mechanisms involved in EMT are far from being fully elucidated. Intratumoral extracellular ATP (eATP), at levels of 100-700 μM or 103 to 104 times higher than in normal tissues, has been known to induce epithelial-mesenchymal-transition (EMT) of cancer cells via purinergic receptor signaling. However, the exact induction mechanisms are far from fully known. We previously described that eATP is internalized by cancer cells in vitro and in vivo by macropinocytosis in human non-small cell lung cancer cells, drastically elevates intracellular ATP levels, enhances cell proliferation and resistance to anticancer drugs. In this study, we tested the hypothesis that eATP and macropinocytosis-internalized eATP also induces EMT and other early steps of metastasis. Here we report that eATP, at the concentrations reported in tumors, potently induces expression of matrix metallopeptidases (MMPs), detachment, EMT, migration, and invasion of lung cancer cells. The induction was independent of TGF-β and semi-independent of P2X7 activation. eATP performs these functions not only extracellularly, but also intracellularly after being macropinocytically internalized to further enhance P2X7-mediated EMT, filopodia formation and other early steps of metastasis. The knockout of the macropinocytosis-associated SNX5 gene significantly reduces macropinocytosis and slows down tumor growth in nude mice. Collectively, these results show that eATP functions on these processes not only from outside of cancer cells but also inside after being macropinocytotically internalized. These findings which shed light on eATP's initiator and effector roles in almost every step in early metastasis call for rethinking and rebalancing energy equations of intracellular biochemical reactions and the Warburg effect, and identify eATP and macropinocytosis as novel targets for potentially slowing down EMT, preventing metastasis, and reducing metastasis-related death in cancer patients. Citation Format: Yanyang Cao, Xuan Wang, Maria Evers, Yunsheng Li, Haiyun Zhang, Xiaozhuo Chen. New roles of ATP in metastasis: Extracellular and macropinocytosis internalized ATP work together to induces epithelial to mesenchymal transition and other early steps of metastasis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1521.

Ibuprofen incorporated into unmodified and modified mesoporous silica: From matrix synthesis to drug release

Abstract Aiming to rationalize the release profile of an incorporated pharmaceutical drug in terms of its mobility, driven by guest-host interactions, the poorly water-soluble Ibuprofen drug was loaded in a mesoporous inorganic silica matrix with unmodified (MCM-41) and modified surface (MCM-41sil) by post-synthesis silylation, both having pore sizes ∼ 3 nm. The single calorimetric detection of a broad glass transition step for both ibuprofen composites indicates full drug amorphization, confirmed by the only appearance of an amorphous halo in the powder XRD patterns. Moreover, a gradient profile is disclosed by the heat flux derivative plot in the glass transition, in coherence with the thermogravimetric profile that shows a multi-step decomposition trace for confined ibuprofen in these matrixes. While identical guest dynamics, as probed by dielectric relaxation spectroscopy, were found in both dehydrated composites, a significant molecular population with faster relaxation exists in the hydrated state for the drug inside the unmodified matrix. This was rationalized as the concurrence of true confinement effects, which manifest under nanometer dimensions, and greater water affinity of the unmodified matrix, forcing the drug molecules to be placed mostly in the pore core. Finite size effects are also felt in both dehydrated composites, however guest-host interactions give origin to a dominant population with slowed down mobility that governs the overall guest dynamics. In spite of an inferior number of active sites for drug adsorption in the silylated matrix, a faster Ibuprofen delivery in phosphate buffer (pH = 6.8) was observed when the drug is released from unmodified MCM-41 in the hydrated state. Therefore, our results suggest that a relevant role is played by water molecules, which impair a strong guest adsorption in the host surface more efficiently than the limited surface modification, influence the higher ratio of a faster population in the pore core and facilitate the diffusion of the aqueous releasing media inside pores.

3072 – MICRORNA-127-3P CONTROLS MURINE HEMATOPOIETIC STEM CELL MAINTENANCE BY LIMITING DIFFERENTIATION

The balance between self-renewal and differentiation is crucial to ensure the homeostasis of the hematopoietic system, and is a hallmark of hematopoietic stem cells. However, the underlying molecular pathways, including the role of micro-RNA, are not completely understood. To assess the contribution of micro-RNA, we performed micro-RNA profiling of hematopoietic stem cells and their immediate downstream progeny multi-potent progenitors from wild-type control and Pbx1-conditional knockout mice, whose stem cells display a profound self-renewal defect. Unsupervised hierarchical cluster analysis separated stem cells from multi-potent progenitors, suggesting that micro-RNA might regulate the first transition step in the adult hematopoietic development. Notably, Pbx1-deficient and wild-type cells clustered separately, linking micro-RNAs to self-renewal impairment. Differential expression analysis of micro-RNA in the physiological stem cell-to-multi-potent progenitor transition and in Pbx1-deficient stem cells compared to control stem cells revealed miR-127-3p as the most differentially expressed. Furthermore, miR-127-3p was strongly stem cell-specific, being quickly down-regulated upon differentiation and not re-expressed further downstream in the bone marrow hematopoietic hierarchy. Inhibition of miR-127-3p function in Lineage-negative cells, achieved through a lentiviral-sponge vector, led to severe stem cell depletion, as assessed with serial transplantation assays. miR-127-3p-sponged stem cells displayed accelerated differentiation, which was uncoupled from proliferation, accounting for the observed stem cell reduction. miR-127-3p over-expression in Lineage-negative cells did not alter stem cell pool size, but gave rise to lymphopenia, likely due to lack of miR-127-3p physiological down-regulation beyond the stem cell stage. Thus, tight regulation of miR-127-3p is crucial to preserve the self-renewing stem cell pool and homeostasis of the hematopoietic system.

Compact Groove Diamond Antenna in Gap Waveguide Technology With Broadband Circular Polarization at Millimeter Waves

In this article, three compact antennas using the ridge gap waveguide (RGW) technology working in the millimeter-wave band (60 GHz), with a high-purity and broadband circular polarization (CP), are numerically and experimentally analyzed. The structure is fed from the bottom by means of a standard WR-15 waveguide (V-band) to make it compatible with standard measurement systems. It is coupled with a miniaturized step transition to a ridgeline that ends in two arms of different lengths. CP is generated in a simple and effective way, by means of two orthogonal feeder arms that excite a CP in a diamond-shaped slot on top. Simulations and measurements have an excellent agreement reaching a matching bandwidth (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> <; -10 dB) from 60.3 to 69.6 GHz (>9 GHz). Applying the axial ratio criterion (AR <; 3 dB) the bandwidth in CP is 14.48%, with respect to the central frequency (60.3-69.6 GHz). The maximum gain is obtained with the most evolved design incorporating a diamond aperture with a horn taper and a circular groove, reaching a value of 11.12 dB at 67.3 GHz.

Computational study of the unimolecular and bimolecular decomposition mechanisms of propylamine

A detailed computational study of the dehydrogenation reaction of trans-propylamine (trans-PA) in the gas phase has been performed using density functional method (DFT) and CBS-QB3 calculations. Different mechanistic pathways were studied for the reaction of n-propylamine. Both thermodynamic functions and activation parameters were calculated for all investigated pathways. Most of the dehydrogenation reaction mechanisms occur in a concerted step transition state as an exothermic process. The mechanisms for pathways A and B comprise two key-steps: H2 eliminated from PA leading to the formation of allylamine that undergoes an unimolecular dissociation in the second step of the mechanism. Among these pathways, the formation of ethyl cyanide and H2 is the most significant one (pathway B), both kinetically and thermodynamically, with an energy barrier of 416 kJ mol−1. The individual mechanisms for the pathways from C to N involve the dehydrogenation reaction of PA via hydrogen ion, ammonia ion and methyl cation. The formation of α-propylamine cation and NH3 (pathway E) is the most favorable reaction with an activation barrier of 1 kJ mol−1. This pathway has the lowest activation energy calculated of all proposed pathways.

Improving double-ended transition state searches for soft-matter systems.

Transitions between different stable configurations of biomolecules are important in understanding disease mechanisms, structure-function relations, and novel molecular-scale engineering. The corresponding pathways can be characterized efficiently using geometry optimization schemes based on double-ended transition state searches. An interpolation is first constructed between the known states and then refined, yielding a band that contains transition state candidates. Here, we analyze an example where various interpolation schemes lead to bands with a single step transition, but the correct pathway actually proceeds via an intervening, low-energy minimum. We compare a number of different interpolation schemes for this problem. We systematically alter the number of discrete images in the interpolations and the spring constants used in the optimization and test two schemes for adjusting the spring constants and image distribution, resulting in a total of 2760 different connection attempts. Our results confirm that optimized bands are not necessarily a good description of the transition pathways in themselves, and further refinement to actually converge transition states and establish their connectivity is required. We see an improvement in the optimized bands if we employ the adjustment of spring constants with doubly-nudged elastic band and a smaller improvement from the image redistribution. The example we consider is representative of numerous cases we have encountered in a wide variety of molecular and condensed matter systems.

Lower Extremity Joint Stiffness And Energy Generation In Gait Transitions

Walk-to-run (WRT) or run-to-walk transitions (RWT) occur when walking at a constantly accelerated speed or running at a constantly decelerated speed. Lower extremity joint level kinetic patterns are related to gait transition mechanisms. Little is known about lower extremity joint stiffness, or mechanical work generation in the WRT and RWT processes. PURPOSE: To identify ankle, knee and hip joint stiffness and mechanical work generation patterns in WRT and RWT processes. METHODS: Ten middle age healthy subjects (50.7 ± 6.0 years, 173.4 ± 11.4 cm, 69.7 ± 14.9 kg) participated in treadmill WRT (1.8 m/s - 2.4 m/s) and RWT (2.4 m/s - 1.8 m/s) tests, with acceleration and deceleration set to 0.1 m/s2 and - 0.1 m/s2, respectively. Five steps were selected for data analysis: transition step (S0); two steps before transition (S-2, S-1); two steps after transition (S1, S2). Joint stiffness (Kjoint) was calculated as change in sagittal plane joint moment (∆Mjoint) divided by sagittal plane joint angular displacement (∆θjoint) in the braking phase of ground contact (Kjoint = ∆Mjoint/∆θjoint). Stance phase joint positive mechanical work (Wjoint+ ) was calculated as the sum of all positive net joint power integrated over time. RESULTS: In WRT, Kankle at S2 was higher than S-2 (p = 0.0004), S-1 (p = 0.0007) and S0 (p = 0.0001); Khip at S1 was higher than S-2 (p = 0.0002) and S-1 (p = 0.0001). In RWT, Kankle at S2 was lower than S-2 (p = 0.0009) and S-1 (p = 0.0006); Khip at S-1 was higher than S1 (p = 0.001) and S2 (p = 0.0003). In WRT stance phase, Wankle+ and Wknee+ were 34% and 60% higher, respectively at S0 compared with S-1; while for Whip+ there was a significant decrease (p = 0.0006) at S0 compared with S-1. In RWT stance phase, Wankle+ and Wknee+ at S0 were 28% and 42% lower than S-1, respectively; while Whip+ at S0 was 78% higher than S-1. CONCLUSIONS: Both WRT and RWT affected Kankle and Khip in the transition step and subsequent steps. Stance phase joint energy generation tended to transfer from proximal to distal during WRT, and vice versa during the RWT process. (Supported by Betty Foster McCue Scholarship.)