Exact solution of mean-field plus an extended T = 1 nuclear pairing Hamiltonian in the seniority-zero symmetric subspace

An extended pairing Hamiltonian that describes multi-pair interactions among isospin T=1 and angular momentum J=0 neutron–neutron, proton–proton, and neutron–proton pairs in a spherical mean field, such as the spherical shell model, is proposed based on the standard T=1 pairing formalism. The advantage of the model lies in the fact that numerical solutions within the seniority-zero symmetric subspace can be obtained more easily and with less computational time than those calculated from the mean-field plus standard T=1 pairing model. Thus, large-scale calculations within the seniority-zero symmetric subspace of the model is feasible. As an example of the application, the average neutron–proton interaction in even–even N∼Z nuclei that can be suitably described in the f5pg9 shell is estimated in the present model, with a focus on the role of np-pairing correlations

Social Capital, Informal Governance, and Post-IPO Firm Performance: A Study of Chinese Entrepreneurial Firms

Presented at Conference on the Sustainable and Ethical Entrepreneurship, Corporate Finance and Governance, and Institutional Reform in China, Beijing, April 6-7, 2013</p

Assessment of continuous fermentative hydrogen and methane co-production using macro- and micro-algae with increasing organic loading rate

A two-stage continuous fermentative hydrogen and methane co-production using macro-algae (Laminaria digitata) and micro-algae (Arthrospira platensis) at a C/N ratio of 20 was established. The hydraulic retention time (HRT) of first-stage H2 reactor was 4 days. The highest specific hydrogen yield of 55.3 mL/g volatile solids (VS) was obtained at an organic loading rate (OLR) of 6.0 gVS/L/d. In the second-stage CH4 reactor at a short HRT of 12 days, a specific methane yield of 245.0 mL/gVS was achieved at a corresponding OLR of 2.0 gVS/L/d. At these loading rates, the two-stage continuous system offered process stability and effected an energy yield of 9.4 kJ/gVS, equivalent to 77.7% of that in an idealised batch system. However, further increases in OLR led to reduced hydrogen and methane yields in both reactors. The process was compared to a one-stage anaerobic co-digestion of algal mixtures at an HRT of 16 days. A remarkably high salinity level of 13.3 g/kg was recorded and volatile fatty acid accumulations were encountered in the one-stage CH4 reactor. The two-stage system offered better performances in both energy return and process stability. The gross energy potential of the advanced gaseous biofuels from this algal mixture may reach 213 GJ/ha/yr

Improved efficiency of anaerobic digestion through direct interspecies electron transfer at mesophilic and thermophilic temperature ranges

Direct interspecies electron transfer (DIET) in microbial communities plays a significant role in improving efficiency of biomethane production from anaerobic digestion. In this study, the impacts of conductive graphene on mesophilic and thermophilic anaerobic digestion (MAD and TAD) were comparatively assessed using the model substrate ethanol. The maximum electron transfer flux for graphene-based DIET was calculated at mesophilic and thermophilic temperatures (35 °C and 55 °C). Biomethane potential results showed that the addition of graphene (1.0 g/L) significantly enhanced biomethane production rates by 25.0% in MAD and 26.4% in TAD. The increased biomethane production was accompanied with enhanced ethanol degradation. The theoretical calculation for maximum DIET flux showed that graphene-based DIET in MAD (76.4 mA) and TAD (75.1 mA) were at the same level, which suggests temperature might not be a significant factor affecting DIET. This slight difference was ascribed to the different Gibbs free energy changes of the overall DIET reaction (CH3CH2OH + 1/2CO2 → 1/2CH4 + CH3COO- + 5H+) in MAD and TAD. Microbial analysis revealed that the dominant microbes in response to graphene addition were distinctly different between MAD and TAD. The results indicated that the bacteria of Levilinea dominated in MAD, while Coprothermobacter dominated in TAD. The abundance of archaeal Methanobacterium decreased, while Methanosaeta increased with increasing temperature

Propulsion Control Technology Development Needs to Address NASA Aeronautics Research Mission Goals for Thrusts 3a and 4

The Commercial Aero-Propulsion Control Working Group (CAPCWG), consisting of propulsion control technology leads from The Boeing Company, GE Aviation, Honeywell, Pratt & Whitney, Rolls-Royce, and NASA (National Aeronautics and Space Administration) Glenn Research Center, has been working together over the past year to identify propulsion control technology areas of common interest that we believe are critical to achieving the challenging NASA Aeronautics Research goals for Thrust 3a: Ultra-Efficient Commercial Vehicles - Subsonic Transports, and Thrust 4: Transition to Alternative Propulsion and Energy. This paper describes the various propulsion control technology development areas identified by CAPCWG as most critical for NASA to invest in. For Thrust 3a these are: i) Integrated On-Board Model Based Engine Control and Health Management; ii) Flexible and Modular Networked Control Hardware and Software Architecture; iii) Intelligent Air/Fuel Control for Low Emissions Combustion; and iv) Active Clearance Control. For Thrust 4a, the focus is on Hybrid Electric Propulsion (HEP) for single aisle commercial aircraft. The specific technology development areas include: i) Integrated Power and Propulsion System Dynamic Modeling for Control; ii) Control Architectures for HEP; iii) HEP Control Verification and Validation; and iv) Engine/Airplane Control Integration. For each of the technology areas, the discussion includes: problem to be solved and how it relates to NASA goals, and the challenges to be addressed in reducing risk

Seed Dormancy, Seedling Establishment and Dynamics of the Soil Seed Bank of \u3cem\u3eStipa Bungeana\u3c/em\u3e (Poaceae) on the Loess Plateau of Northwestern China

Studying seed dormancy and its consequent effect can provide important information for vegetation restoration and management. The present study investigated seed dormancy, seedling emergence and seed survival in the soil seed bank of Stipa bungeana, a grass species used in restoration of degraded land on the Loess Plateau in northwest China. Dormancy of fresh seeds was determined by incubation of seeds over a range of temperatures in both light and dark. Seed germination was evaluated after mechanical removal of palea and lemma (hulls), chemical scarification and dry storage. Fresh and one-year-stored seeds were sown in the field, and seedling emergence was monitored weekly for 8 weeks. Furthermore, seeds were buried at different soil depths, and then retrieved every 1 or 2 months to determine seed dormancy and seed viability in the laboratory. Fresh seeds (caryopses enclosed by palea and lemma) had non-deep physiological dormancy. Removal of palea and lemma, chemical scarification, dry storage (afterripening), gibberellin (GA3) and potassium nitrate (KNO3) significantly improved germination. Dormancy was completely released by removal of the hulls, but seeds on which hulls were put back to their original position germinated to only 46%. Pretreatment of seeds with a 30% NaOH solution for 60 min increased germination from 25% to 82%. Speed of seedling emergence from fresh seeds was significantly lower than that of seeds stored for 1 year. However, final percentage of seedling emergence did not differ significantly for seeds sown at depths of 0 and 1 cm. Most fresh seeds of S. bungeana buried in the field in early July either had germinated or lost viability by September. All seeds buried at a depth of 5 cm had lost viability after 5 months, whereas 12% and 4% seeds of those sown on the soil surface were viable after 5 and 12 months, respectively

Improving gaseous biofuel production from seaweed Saccharina latissima: the effect of hydrothermal pretreatment on energy efficiency

Marine macroalgae (seaweed) is a promising feedstock for producing biohydrogen and biomethane via dark fermentation and anaerobic digestion, respectively. However, one of the limiting steps in the biological process is the conversion of polymeric carbohydrates into monomeric sugars. Here hydrothermal pretreatments were assessed for hydrolysis and subsequent production of biohydrogen and biomethane from the brown seaweed Saccharina latissima. The solubilization of S. latissima improved with increasing temperatures from 100 to 180 °C, resulting in a maximum yield of 0.70 g soluble chemical oxygen demand/gram volatile solid (sCOD/g VS); equivalent to an increase of 207.5% compared with untreated seaweed. However, the yield of the derived monomeric sugar mannitol peaked at 140 °C and decreased with increasing temperatures, likely due to production of fermentative inhibitors. Microstructural characterization revealed that the algal structure was significantly damaged, and the major chemical groups of carbohydrates and proteins were weakened after pretreatment. Regardless of hydrothermal temperatures, biohydrogen yield only slightly increased in dark fermentation, while biomethane yield significantly increased from 281.4 (untreated S. latissima) to 345.1 mL/g VS (treated at 140 °C), leading to the sCOD removal efficiency of 86.1%. The maximum energy conversion efficiency of 72.8% was achieved after two-stage biohydrogen and biomethane co-production. In comparison, considering the energy input for pretreatment/fermentation/digestion, the highest process energy efficiency dropped to 37.8%. Further calculations suggest that a significant improvement of efficiency up to 56.9% can be achieved if the heat from pretreatment can be recovered

Observation of oscillatory relaxation in the Sn-terminated surface of epitaxial rock-salt SnSe {111}\{111\} topological crystalline insulator

Topological crystalline insulators have been recently predicted and observed in rock-salt structure SnSe $\{111\}$ thin films. Previous studies have suggested that the Se-terminated surface of this thin film with hydrogen passivation, has a reduced surface energy and is thus a preferred configuration. In this paper, synchrotron-based angle-resolved photoemission spectroscopy, along with density functional theory calculations, are used to demonstrate conclusively that a rock-salt SnSe $\{111\}$ thin film epitaxially-grown on \ce{Bi2Se3} has a stable Sn-terminated surface. These observations are supported by low energy electron diffraction (LEED) intensity-voltage measurements and dynamical LEED calculations, which further show that the Sn-terminated SnSe $\{111\}$ thin film has undergone a surface structural relaxation of the interlayer spacing between the Sn and Se atomic planes. In sharp contrast to the Se-terminated counterpart, the observed Dirac surface state in the Sn-terminated SnSe $\{111\}$ thin film is shown to yield a high Fermi velocity, $0.50\times10^6$m/s, which suggests a potential mechanism of engineering the Dirac surface state of topological materials by tuning the surface configuration.Comment: 12 pages, 13 figures, supplementary materials include