Fluid Models of Parallel Service Systems Under FCFS

In parallel service systems, customers of various types are served simultaneously by several servers that have some dierent and some overlapping skills or capacities. Examples include customer routing in call centers, scheduling of hospital operating rooms, and driver assignment in ride-hailing services. First come first served (FCFS) is a natural and widespread resource allocation policy, yet its performance both during the transient stage and in the long run is often difficult to analyze. In particular, matching rates, which indicate what fraction from all services are of a specific server customer type, are difficult to evaluate under FCFS. In Fluid Models of Parallel Service Systems under FCFS, Yuval Nov, Gideon Weiss, and Hanqin Zhang formulate a stochastic queueing model for such systems and study its fluid approximation. The paper demonstrates the usefulness and the limitations of exploring fluid performance in evaluating system behavior in terms of stability, responsiveness, and utilization.

Effect of minor Nb on isothermal-oxidation and hot corrosion behavior of two Nickel-based superalloys under Na2SO4 / Na2SO4-NaCl

Two nickel-based superalloys with and without minor Nb were prepared using double vacuum melting. The comparison of microstructure, isothermal-oxidation and hot corrosion behavior under molten Na2SO4 / Na2SO4+25wt. % NaCl at 900 C was evaluated. Results indicated that Nb accelerated the formation of chromia scale in a short transient stage, leading to a lower scaling rate. Nb also inhibited the internal oxidation/ nitridation. Both significantly improved the hot corrosion resistance under Na2SO4. However, the beneficial effect of Nb is slight under mixed salts with NaCl. The beneficial effects of Nb on oxidation and hot corrosion are discussed in detail.

Severity and Duration of Acute Kidney Injury and Chronic Kidney Disease after Cardiac Surgery

We aimed to evaluate whether the duration and stage of acute kidney injury (AKI) are associated with the occurrence of chronic kidney disease (CKD) in patients undergoing cardiac or thoracic aortic surgery. A total of 2009 cases were reviewed. The patients with postoperative AKI stage 1 and higher stage were divided into transient (serum creatinine elevation ≤48 h) or persistent (>48 h) AKI, respectively. Estimated glomerular filtration rate (eGFR) values during three years after surgery were collected. Occurrence of new-onset CKD stage 3 or higher or all-cause mortality was determined as the primary outcome. Multivariable Cox regression and Kaplan–Meier survival analysis were performed. The Median follow-up of renal function after surgery was 32 months. The cumulative incidences of our primary outcome at one, two, and three years after surgery were 19.8, 23.7, and 26.1%. There was a graded significant association of AKI with new-onset CKD during three years after surgery, except for transient stage 1 AKI (persistent stage 1: HR 3.11, 95% CI 2.62–4.91; transient higher stage: HR 4.07, 95% CI 2.98–6.11; persistent higher stage: HR 13.36, 95% CI 8.22–18.72). There was a significant difference in survival between transient and persistent AKI at the same stage. During three years after cardiac surgery, there was a significant and graded association between AKI stages and the development of new-onset CKD, except for transient stage 1 AKI. This association was stronger when AKI lasted more than 48 h at the same stage. Both duration and severity of AKI provide prognostic value to predict the development of CKD.

The Prevalence of Ureaplasma Urealyticum and Mycoplasma Hominis Infections in Infertile Patients in the Northeast Region of Romania

Background and objectives: Ureaplasma urealyticum (UU) and Mycoplasma hominis (MH) are two commensal microorganisms that form the urogenital microbiota. Under a state of dysbiosis, both bacteria cause intrauterine infection. Material and methods: Therefore, the purpose of the present study was to analyze the prevalence of UU and MH among four hundred and eleven infertile women. Results: Women between thirty and thirty-five years old were the most affected group, followed by those that were 25 and 30 years old, respectively. Cumulatively, the prevalence of single UU and MH, and coinfection, was 28.46% (n = 117), (n = 2) 0.48%, and 2.91% (n = 12), respectively, with an overall detection rate of 31.87% (n = 131). To assess the associated drug susceptibility, endocervical samples were unequally sent to Regina Maria (n = 281) and Synevo (n = 130) laboratories for further analyses. Pristinamycin (100% vs. 100%) and Josamycin (100% vs. 98.00%) were the most efficient antibiotics in eradicating UU and MH, several others also displaying a high efficiency, among which can be mentioned Doxycycline (98.23%), Minocycline (96.00%), Tetracycline (96.48% vs. 68.00%), and Erythromycin (70.17% vs. 92.00%). Based on antibiograms, Clarithromycin (88.00%), Roxithromycin (88.00%), Levofloxacin (82.00%), and Azithromycin (78.94%) can be further used in treating such infections. On the other hand, Clindamycin (4.00%) and Ciprofloxacin (12.27% vs. 2.00%) are no longer viable because both UU and MH display an intermediate response towards gained resistance. Interestingly, the efficiency of Ofloxacin (22.79% vs. 60.00%) was conflicting, this possibly suggesting a transient stage to a gradual adaptability of these microorganisms to Ofloxacin. Conclusions: The most susceptible age groups in each case were women that were between twenty and forty years old. It can be concluded that four antibiotics can be safely used for treating UU, MH, or dual infections whose efficiency was over 95%.

Numerical Analysis of Oxygen Vacancy Distribution in Semiconductor Gas Sensors in the Cooling Process Based on the Model of Gradient-Distributed Oxygen Vacancies

The oxygen vacancies (VO) play an essential role in the gas-sensing mechanism of semiconductor devices. A diffusion equation is established to describe the VO behaviors during a cooling process based on the model of gradient-distributed oxygen vacancies. Numerical solutions of the diffusion equation are found to illustrate the VO distribution in grains. The gradient of VO distribution is of negative dependence on the cooling rate, which also influences the average VO density in the depletion layer. The migration of oxygen vacancies in cooling process could be interrupted by quenching and it is restarted by the re-annealing process. The VO distributing process is illustrated by three stages from initial uniform distribution to final gradient profile via a transient stage. The influence of VO distribution on gas-sensing characteristics of semiconductor grains is discussed. Potential opportunities are found to control the gas sensor characteristics by a designed annealing process.

Phantom energy-dominated universe as a transient stage in f(R) cosmology

The [Formula: see text] theories of gravity are the most popular, simple and well-succeeded extension of Einstein’s General Relativity. They can account for some observational issues of standard cosmology with no need for evoking the dark sector of the universe. In the present paper, we will investigate LRS Bianchi type-I spacetime in [Formula: see text] gravity theory within the phantom energy-dominated era. We show that in this formalism the phantom energy-dominated universe is a transient stage and in the further stage of the universe dynamics, it is dominated, once again, by dark energy. Such an important feature is obtained from the model, rather than imposed to it, and may have a relation to loop quantum cosmology.

Improving subduction interface implementation in dynamic numerical models

Numerical subduction models often implement an entrained weak layer (WL) to facilitate decoupling of the slab and upper plate. This approach is attractive in its simplicity, and can provide stable, asymmetric subduction systems that persist for many tens of millions of years. In this study we undertake a methodological analysis of the WL approach, and use these insights to guide improvements to the implementation. The issue that primarily motivates the study is the emergence of significant spatial and temporal thickness variations within the WL. We show that these variations are mainly the response to volumetric flux gradients, caused by the change in boundary conditions as the WL material enters and exits the zone of decoupling. The time taken to reach a quasi-equilibrium thickness profile will depend on the total plate convergence, and is around 7 Myr for the models presented here. During the transient stage, width variations along the WL can exceed 4×, which may impact the effective strength of the interface, through physical effects if the rheology is linear, or simply if the interface becomes inadequately numerically resolved. The transient stage also induces strong sensitivity to model resolution. By prescribing a variable-thickness WL at the outset of the model, and by controlling the limits of the layer thickness during the model evolution, we find improved stability and resolution convergence of the models.

A Fast Simulation Method for Damaged Ship Dynamics

Ship accidents that entail flooding may lead to disastrous consequences which could be avoided or mitigated based on the knowledge of damaged ship dynamics. The dynamic behaviour of a damaged hull is a complex phenomenon involving the interaction of the flooded water and the ship motions. The presence of a damage opening allows water flow into and out from the compartment, which further complicates the mathematical description of the problem. A fast simulation method, based on the lumped mass approach, is developed and presented. The lumped mass path in space depends on free-surface inclinations that differ from the ship angles of the roll and pitch. The viscous effects in the floodwater dynamics are implemented based on the model for the dissipation of the energy of standing waves in rectangular rooms. The method applies to both the transient stage of flooding and to the dynamic behaviour of a flooded ship in regular waves. In the first case, viscous effects are implemented considering the water in the compartment variable with time. Several case studies are carried out on three different hull models: Transient stage of flooding, roll decay of the damaged hull, and steady state responses in waves are simulated and compared with available experimental data.