Catalytic Mechanism of Bacteriophage T4 Rad50 ATP Hydrolysis

Spontaneous double-strand breaks (DSBs) are one of the most deleterious forms of DNA damage, and their improper repair can lead to cellular dysfunction. The Mre11 and Rad50 proteins, a nuclease and an ATPase, respectively, form a well-conserved complex that is involved in the initial processing of DSBs. Here we examine the kinetic and catalytic mechanism of ATP hydrolysis by T4 Rad50 (gp46) in the presence and absence of Mre11 (gp47) and DNA. Single-turnover and pre-steady state kinetics on the wild-type protein indicate that the rate-limiting step for Rad50, the MR complex, and the MR-DNA complex is either chemistry or a conformational change prior to catalysis. Pre-steady state product release kinetics, coupled with viscosity steady state kinetics, also supports that the binding of DNA to the MR complex does not alter the rate-limiting step. The lack of a positive deuterium solvent isotope effect for the wild type and several active site mutants, combined with pH–rate profiles, implies that chemistry is rate-limiting and the ATPase mechanism proceeds via an asymmetric, dissociative-like transition state. Mutation of the Walker A/B and H-loop residues also affects the allosteric communication between Rad50 active sites, suggesting possible routes for cooperativity between the ATP active sites

Heat pump integration for total site waste heat recovery

Total Site Heat Integration (TSHI) promotes energy recovery between processes to enhance overall energy efficiency of an industrial complex. Various industrial wast e heat utilisation technologies have been studied to improve the energy efficiency of energy system. Vapour compression as an open loop heat pump system has good potential to be used to upgrade the waste heat to us eful heat in Total Site systems. Vapour compression systems upgrade low grade waste heat by supplying a low quantity of high pressure steam (thermo- compressor) or mechanical work (mechanical-compressor) to generate higher pressure steam, as is common with evaporation systems. The vapour compression system recovers the latent heat content of the industrial waste heat, which reduces cooling demand, decreasing the demand for high quality steam and reducing boiler load. This paper introduces an effective Total Site targeting methodology to integrate open cycle heat pump systems, i.e. vapour compression technologies, into an integrated industrial energy system for enhancing overall site energy efficiency. Industrial waste heat and high quality steam demand are able to be reduced simultaneously though this integrat ion. The energy reduction and cost- benefit of thermo-compressor and mechanical-compressor installations are compared through a literature case study. The case study showed a deficit of heat at the M PS and a surplus of heat the LPS, which wa s identified as a candidate for compression according to the appropriate placement principle for heat pumps. For the case study, a four-stage mechanical vapour compression system and two-stage thermal vapour compression system resulted in an energy cost reductions of 343,859 USD/y and 168,829 USD/y

A unified total site heat integration targeting method for isothermal and non-isothermal utilities

This paper presents a new unified Total Site Heat Integration (TSHI) targeting methodology that calculates improved TSHI targets for sites that requires isothermal (e.g. steam) and non-isothermal (e.g. hot water) utilities. The new method sums process level utility targets to form the basis of Total Site utility targets; whereas the conventional method uses Total Site Profiles based excess process heat deficits/surpluses to set Total Site targets. Using an improved targeting algorithm, the new method requires a utility to be supplied to and returned from each process at specified temperatures, which is critical when targeting non-isothermal utilities. Such a constraint is not inherent in the conventional method. The subtle changes in procedure from the conventional method means TSHI targets are generally lower but more realistic to achieve. Three industrial case studies representing a wide variety of processing industries, are targeted using the conventional and new TSHI methods, from which key learnings are found. In summary, the over-estimation of TSHI targets for the three case studies from using the conventional method compared to new method are 69% for a New Zealand Dairy Factory, 8% for the Södra Cell Värö Kraft Pulp Mill, and 12% for Petrochemical Complex

Assisted heat transfer and shaft work targets for increased total site heat integration

Total Site Heat Integration (TSHI) provides a valuable framework for practical integration of multiple energy users. Previous studies have introduced the idea of utilising process heat recovery pockets to assist TSHI. However, these methods are shown to be effective for only some Total Site (TS) problems. As a result, this paper presents a new method for calculating assisted heat transfer and shaft work targets for an example TS problem. Analysis results show that assisted heat transfer increases TSHI only when a process heat recovery pocket spans the TS Pinch Region. The maximum assisted TSHI can be targeted by comparing each heat recovery pocket to the Site Utility Grand Composite Curve (SUGCC) using background/foreground analysis. Where heat recovery pockets span two steam pressure levels away from the TS Pinch Region (usually above), the example shows the potential for assisted shaft work production. In this case, the source segment of the heat recovery pocket generates steam (e.g. MPS), which replaces steam that would otherwise have been extracted from a steam turbine. The sink segment of the heat recovery pocket consumes lower pressure steam (e.g. LPS), which is extracted from the turbine. If a heat recovery pocket falls outside these two situations (assuming direct inter - process integration is disallowed), the entire pocket should be recovered internal to a process

Optimization of Cooling Utility System with Continuous Self-Learning Performance Models

Prerequisite for an efficient cooling energy system is the knowledge and optimal combination of different operating conditions of individual compression and free cooling chillers. The performance of cooling systems depends on their part-load performance and their condensing temperature, which are often not continuously measured. Recorded energy data remain unused, and manufacturers’ data differ from the real performance. For this purpose, manufacturer and real data are combined and continuously adapted to form part-load chiller models. This study applied a predictive optimization algorithm to calculate the optimal operating conditions of multiple chillers. A sprinkler tank offers the opportunity to store cold-water for later utilization. This potential is used to show the load shifting potential of the cooling system by using a variable electricity price as an input variable to the optimization. The set points from the optimization have been continuously adjusted throughout a dynamic simulation. A case study of a plastic processing company evaluates different scenarios against the status quo. Applying an optimal chiller sequencing and charging strategy of a sprinkler tank leads to electrical energy savings of up to 43%. Purchasing electricity on the EPEX SPOT market leads to additional costs savings of up to 17%. The total energy savings highly depend on the weather conditions and the prediction horizon

Effect of solar utility temperature to costing and design parameters of integrated solar thermal system

The objective of this research is to evaluate the trade - off between solar utility temperature and solar collector efficiency, in the context of Malaysia, and also evaluating the proposed system efficiency and economic feasibility. Since Malaysia receives an abundance amount of solar radiation throughout the year, generating thermal energy from solar thermal energy system is highly attractive. In the illustrative case study, flat plate collector (FPC) and compound parabolic collector (CPC) were used for evaluation of integration with different temperature process . For each process, configuration with and without HEX were evaluated. Generally, solar collector cost for configuration with HEX is more than configuration without HEX , solar collector cost will be lower when solar utility temperature is lower , and effect of solar utility temperature variation affect more on FPC than on CPC. The results show that annual saving is 174,952 MYR /y . The payback period for all processes vary from 4.7 to 7.6 y