For heterotrophic microbes, limited availability of carbon and energy sources is one of the major nutritional factors restricting the rate of growth in most ecosystems. Physiological adaptation to ...this hunger state requires metabolic versatility which usually involves expression of a wide range of different catabolic pathways and of high-affinity carbon transporters; together, this allows for simultaneous utilization of mixtures of carbonaceous compounds at low concentrations. In Escherichia coli the stationary phase sigma factor RpoS and the signal molecule cAMP are the major players in the regulation of transcription under such conditions; however, their interaction is still not fully understood. Therefore, during growth of E. coli in carbon-limited chemostat culture at different dilution rates, the transcriptomes, expression of periplasmic proteins and catabolomes of strains lacking one of these global regulators, either rpoS or adenylate cyclase (cya), were compared to those of the wild-type strain. The inability to synthesize cAMP exerted a strong negative influence on the expression of alternative carbon source uptake and degradation systems. In contrast, absence of RpoS increased the transcription of genes belonging to high-affinity uptake systems and central metabolism, presumably due to reduced competition of σ(D) with σ(S). Phenotypical analysis confirmed this observation: The ability to respire alternative carbon substrates and to express periplasmic high-affinity binding proteins was eliminated in cya and crp mutants, while these properties were not affected in the rpoS mutant. As expected, transcription of numerous stress defence genes was negatively affected by the rpoS knock-out mutation. Interestingly, several genes of the RpoS stress response regulon were also down-regulated in the cAMP-negative strain indicating a coordinated global regulation. The results demonstrate that cAMP is crucial for catabolic flexibility during slow, carbon-limited growth, whereas RpoS is primarily involved in the regulation of stress response systems necessary for the survival of this bacterium under hunger conditions.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•Solar Rankine Cycle (SRC) and Integrated Solar Combined Cycle (ISCC) were compared.•Solar fields based on parabolic trough and power tower systems were examined.•Parabolic troughs have a worse ...collection efficiency than solar tower.•ISCC with solar tower provides the highest solar-to-electric efficiency.•Both ISCC and SRC plants with parabolic troughs are much less performing.
Simulations were carried out to predict the performance of a Solar Rankine Cycle (SRC) and an Integrated Solar Combined Cycle (ISCC) when combined with two different solar field configurations based on parabolic trough and power tower systems. For the selected cases, yearly plant performance was computed under real operating conditions on a one hour basis. A computing procedure was developed by integrating two commercial softwares with in-house computer code. Thermodynamic performance was featured for every plant configuration both at nominal and part load conditions. A single reheat regenerative Rankine cycle was chosen for the SRC plant whereas a commercial gas turbine, i.e. Siemens SGT-800, with a dual pressure heat recovery steam generator (HRSG) was assumed for the ISCC plant. As far as the heat transfer fluid (HTF) is concerned, molten salt was chosen to transfer heat to the water loop in the SRC. Synthetic oil was considered in the ISCC plant. Plants were assumed to be located in a Southern Spain site.
The comparative analysis was mainly focused on the influence of CSP technology on global solar energy conversion efficiency of both SRC and ISCC plants. Special attention was devoted to assess trough collectors (PTCs) against the solar tower (ST) system in terms of intercepted radiation and thermal power sent to the power block. The ISCC coupled with a ST was found to assure the highest annual solar-to-electric efficiency of 21.8%. This is the result of both higher collection efficiency of ST compared to PTCs and higher conversion efficiency of solar energy introduced into the combined cycle, as compared to SRC.
•The operation of solar district cooling systems is investigated.•The optimal size of each component is determined for the primary cost minimization.•Efficiency of 2-stage chiller with PTC is higher ...than 1-stage chiller with ETC.•Plant configuration based on PTC and 2-stage chiller is more cost effective (−30%).
The present paper aims to evaluate the performance of a solar district cooling system in typical Middle East climate conditions. A centralized cooling station is supposed to distribute chilled water for a residential compound through a piping network. Two different solar cooling technologies are compared: two-stage lithium-bromide absorption chiller (2sABS) driven by Parabolic Trough Collectors (PTCs) vs. single-stage lithium-bromide absorption chiller (1sABS) fed by Evacuated Tube Collectors (ETCs). A computer code has been developed in Trnsys® (the transient simulation software developed by the University of Wisconsin) to simulate on hourly basis the annual operation of the solar cooling system, including building thermal load calculation, thermal losses in pipes and control strategy of the energy storage. A solar fraction of 70% was considered to size the solar field aperture area and the chiller capacity, within a multi-variable optimization process. An auxiliary compression chiller is supposed to cover the peak loads and to be used as backup unit. The two different solar cooling plants exhibit strongly different performance. For each plant configuration, the model determined the optimal size of every component leading to the primary cost minimization. The solar district cooling configuration based on 2sABS and PTCs shows higher performance at Riyadh (KSA) climate conditions and the overall cost is 30% lower than the one of the single-stage absorption chiller plant.
•The design and the construction of the first Eenrgy+ autonomous building in Dubai is presented.•A 40 kWp PV field coupled with a 48 kWh electric storage makes the building energy-autonomous ...24/7.•The internal comfort is assured by a solar cooling system, without power import from the grid.•Thermal envelope and energy systems are fully instrumented: the monitored perfomance is in very good agreement with the model prediction.
This work presents the measured performance data related to the very-first Energy+ building in Dubai certified by the Passive House Institute. The building is a two-floor office structure, with 550 m2 total surface, designed under the guide and the scientific supervision of a Bergamo University research group, jointly to the Mohammed Bin Rashid Space Centre (MBRSC). The goal of the project was to assure a high level of internal comfort all over the year by using only solar energy. The building architecture has been designed to minimize the cooling load and the energy demand. The energy system is based on a 40 kWp PV field coupled with a 48 kWh electric storage and a high-efficiency chiller (reversible heat pump). Transient simulations by Trnsys code have been carried out to optimize both the thermal envelope and the energy plants so to make the building energy-autonomous 24/7. The numerical predictions of the energy performance (including cooling load, PV production and power consumption for chiller, lighting and appliances) are compared to the real data measured by a sophisticated monitoring system, including sensors located in the roof, in the external walls and in the energy systems. The field measurements confirm that the model predictions were accurate both in terms of peak and annual values. The small variations between prediction and real data show that both thermal envelope and PV field perform better than expected.
This building is a pioneering pilot-project: the goal was to show that new sustainable construction standards using only solar energy are possible in the United Arab Emirates (UAE) and that this is a viable solution to reduce the carbon footprint in all the Gulf region. The strategic importance of an accurate modeling activity leading to an optimal design has been proved. The monitored data under real operating conditions have confirmed that the expected targets in terms of energy savings and carbon footprint reduction have been successfully achieved.
Abstract
The target of a Renewable Energy Community (REC) is to improve the renewable energy consumption without forcing the grid to work as a power backup and avoid the installation of large energy ...storage systems. The paper proposes a comparison between different REC configurations with the same annual energy consumption of 500 MWh corresponding to about 200 residential houses in northern Italy. The comparison includes different kinds of building destination (residential, commercial, industrial), and different photovoltaic (PV) installed capacity. The results highlight the fundamental role of a proper design of the Renewable Energy Community configuration. RECs based on members with complementary loads enhance the renewable energy consumption by increasing the fraction of shared energy. Different roles (consumer and prosumer) are fundamental to provide the proper energy distribution during the sunny hours by producing a win-win condition. Nevertheless, an increase of the PV capacity can produce a detrimental effect on the shared energy ratio due the non-contemporaneity of production and consumption.
We compute the modified friction coefficient controlling the propagation of tensor metric perturbations in the context of a generalized cosmological scenario based on a theory of gravity with ...quadratic curvature corrections. In such a context we discuss the differences between gravitational and electromagnetic luminosity distance, as well as the differences with the standard results based on the Einstein equations. We present numerical estimates of the modified luminosity distance on the cosmic redshift scale typical of Supernovae and standard sirens.
The present paper deals with the performance prediction of Concentrated Solar Power plants integrated with cooling energy production. The plant configuration is based on a typical steam Rankine cycle ...(rated 62.1 MWe). The thermal input is provided by two different solar fields: i) Parabolic Trough Collectors and ii) Central Receiver System with heliostats reflecting on the tower top. In the former case, both north-south and east-west oriented collectors are investigated and compared in the study. A Thermal Energy Storage system allows driving the power block 24-h per day also in periods with low solar irradiation. A steam flow rate extracted from the turbine low stages feeds a set of two-stage absorption chillers, and the produced chilled water is supplied to a district cooling network. A computer code integrating the commercial software Thermoflex and Trnsys has been developed to model and to simulate over 1-year period the solar field and the power block.
The power plant is supposed to operate in island mode, having to meet power and cooling demand for a population of about 50,000 inhabitants in the Saudi desert region. Solar fields and storage system were sized according to a techno-economic optimization algorithm for the minimization of the investment costs. The simulation results show the beneficial effect of the combined power and cooling production in terms of peak load shaving. Compared to the troughs, solar tower exhibits a higher efficiency, thus requiring a lower aperture area and lower investment costs. The techno-economic analysis shows that the axis orientation has a strong impact on the trough collectors and that east-west oriented devices perform better for the investigated load-following application.
•A solar driven Rankine cycle, with cooling production, was simulated in island mode.•Parabolic troughs and heliostat field with central receiver were assessed.•North-south aligned parabolic troughs required the largest aperture area.•Heliostats, with the lowest aperture area, provided the lowest thermal energy surplus.•Heliostats with central receiver are the best solution in load-following operation.
LEOPARD syndrome (LS) is an autosomal dominant "RASopathy" that manifests with congenital heart disease. Nearly all cases of LS are caused by catalytically inactivating mutations in the protein ...tyrosine phosphatase (PTP), non-receptor type 11 (PTPN11) gene that encodes the SH2 domain-containing PTP-2 (SHP2). RASopathies typically affect components of the RAS/MAPK pathway, yet it remains unclear how PTPN11 mutations alter cellular signaling to produce LS phenotypes. We therefore generated knockin mice harboring the Ptpn11 mutation Y279C, one of the most common LS alleles. Ptpn11(Y279C/+) (LS/+) mice recapitulated the human disorder, with short stature, craniofacial dysmorphia, and morphologic, histologic, echocardiographic, and molecular evidence of hypertrophic cardiomyopathy (HCM). Heart and/or cardiomyocyte lysates from LS/+ mice showed enhanced binding of Shp2 to Irs1, decreased Shp2 catalytic activity, and abrogated agonist-evoked Erk/Mapk signaling. LS/+ mice also exhibited increased basal and agonist-induced Akt and mTor activity. The cardiac defects in LS/+ mice were completely reversed by treatment with rapamycin, an inhibitor of mTOR. Our results demonstrate that LS mutations have dominant-negative effects in vivo, identify enhanced mTOR activity as critical for causing LS-associated HCM, and suggest that TOR inhibitors be considered for treatment of HCM in LS patients.
Lipid-binding proteins (LBPs) are soluble proteins responsible for the uptake, transport, and storage of a large variety of hydrophobic lipophilic molecules including fatty acids, steroids, and other ...lipids in the cellular environment. Among the LBPs, fatty acid binding proteins (FABPs) present preferential binding affinities for long-chain fatty acids. While most of FABPs in vertebrates and invertebrates present similar β-barrel structures with ligands accommodated in their central cavity, parasitic nematode worms exhibit additional unusual α-helix rich fatty acid- and retinol-binding proteins (FAR). Herein, we report the comparison of extended molecular dynamics (MD) simulations performed on the ligand-free and palmitic acid-bond states of the Necator americanus FAR-1 (Na-FAR-1) with respect to other classical β-barrel FABPs. Principal component analysis (PCA) has been used to identify the different conformations adopted by each system during MD simulations. The α-helix fold encompasses a complex internal ligand-binding cavity with a remarkable conformational plasticity that allows reversible switching between distinct states in the holo-Na-FAR-1. The cavity can change up to one-third of its size affected by conformational changes of the protein–ligand complex. Besides, the ligand inside the cavity is not fixed but experiences large conformational changes between bent and stretched conformations. These changes in the ligand conformation follow changes in the cavity size dictated by the transient protein conformation. On the contrary, protein–ligand complex in β-barrel FABPs fluctuates around a unique conformation. The significantly more flexible holo-Na-FAR-1 ligand-cavity explains its larger ligand multiplicity respect to β-barrel FABPs.
Abstract
The present work proposes a comparison between three solar-powered district heating and cooling systems, namely: 1) centralized district heating & cooling (DHC) system; 2) 5th-generation ...district heating & cooling (5GDHC) system and 3) individual AC plants (HHC, Home Heating and Cooling), in different climate conditions. Thermal loads are evaluated by transient simulations of a residential compound featuring 56 detached houses for three different Italian climates: (1) a Mediterranean region on the seaside (Palermo, I), (2) a temperate climate in Central Italy (Roma, I), and (3) a cold-temperate climate in Northern Italy (Bolzano, I). The DHC system shows the highest efficiency in terms of energy-savings, whatever the location. The 5GDHC system reaches a compromise between installation and operational costs.
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