Molecular-dynamics study of multi-pulsed ultrafast laser interaction with copper

Ultrafast laser has an undeniable advantage in laser processing due to its extremely small pulse width and high peak energy. While the interaction of ultrafast laser and solid materials is an extremely non-equilibrium process in which the material undergoes phase transformation and even ablation in an extremely short time range. This is the coupling of the thermos elastic effect caused by the pressure wave and the superheated melting of the material lattice. To further explore the mechanism of the action of ultrafast laser and metal materials, the two-temperature model coupling with molecular dynamics method was used to simulate the interaction of the copper and laser energy. Firstly, the interaction of single-pulsed laser and copper film was reproduced, and the calculated two-temperature curve and the visualized atomic snapshots were used to investigate the influence of laser parameters on the ablation result. Then, by changing the size of the atomic system, the curve of ablation depth as a function of laser fluence was obtained. In this paper, the interaction of multi-pulsed laser and copper was calculated. Two-temperature curve and temperature contour of copper film after the irradiation of double-pulsed and multi-pulsed laser were obtained. And the factors which can make a difference to the incubation effect were analyzed. By calculating the ablation depth under the action of multi-pulsed laser, the influence of the incubation effect on ablation results was further explored. Finally, a more accurate numerical model of laser machining metal is established and verified by an ultra-short laser processing experiment, which provides a new calculation method and theoretical basis for ultra-fast laser machining of air film holes in aviation turbine blades, and has certain practical guiding significance for laser machining.

RETROSPECTIVE ANALYSIS OF ACUTE LYMPHADENITIS OF THE MAXILLOFACIAL REGION AND NECK IN CHILDREN

Дети с острыми формами лимфаденитов челюстно-лицевой области составляют большую часть пациентов поликлиник и профильных стационаров. Зачастую они имеют недооцененную клиническую картину, общее состояние, распространенность и динамику острого воспалительного процесса, требуя хирургического вмешательства. Допущенные ошибки приводят к удлинению сроков лечения и иногда угрозе для жизни. Для раннего выявления показаний для госпитализации и помощи практикующим врачам в алгоритме действий проведен анализ случаев острых лимфаденитов лица и шеи в детском возрасте. На основе ретроспективных данных осуществлена систематизация лимфаденитов челюстно-лицевой области по клиническим формам и распределении частоты встречаемости, возрасту, анатомической принадлежности, выделены основные изменения гематологических показателей. Определена корреляция температурной кривой, этиологические причины возникновения лимфаденитов и основные микробиологические возбудители гнойных форм лимфаденитов лица и шеи у детей. На основании полученных данных нами разработаны и предложены критерии дифференциальной диагностики разных клинических форм лимфаденита, что поможет врачу с постановкой предварительного диагноза, или дифференциальной диагностике, на этапе поликлиники или на догоспитальном приёме. Данные критерии помогут сократить сроки лечения детей в стационаре и не допустить развития тяжелых осложнений Children with acute forms of lymphadenitis of the maxillofacial region make up the majority of patients in polyclinics and specialized hospitals. They often have an underestimated clinical picture, general condition, prevalence and dynamics of an acute inflammatory process, requiring surgical intervention. Mistakes lead to lengthening of treatment and sometimes life-threatening. For early detection of indications for hospitalization and assistance to practitioners in the algorithm of actions, an analysis of cases of acute lymphadenitis of the face and neck in childhood was carried out. On the basis of retrospective data, the systematization of lymphadenitis of the maxillofacial region by clinical forms and distribution of frequency of occurrence, age, anatomical affiliation was carried out, the main changes in hematological parameters were highlighted. The correlation of the temperature curve, the etiological causes of the occurrence of lymphadenitis and the main microbiological pathogens of purulent forms of lymphadenitis of the face and neck in children were determined. Based on the data obtained, we have developed and proposed criteria for the differential diagnosis of various clinical forms of lymphadenitis, which will help the doctor with a preliminary diagnosis, or differential diagnosis, at the stage of the polyclinic or at the pre-hospital admission. These criteria will help to shorten the period of hospital treatment for children and prevent the development of severe complications

Minimum design metal temperature of Q345R determined by exemption curve in ASME VIII-2 and its derived methods

In order to prevent the brittle fracture accident, minimum design metal temperature of ferrite steel should be limited. After the minimum design metal temperature curve in American Society of Mechanical Engineers VIII-2 (2007) was proposed, much related research has been done in recent years. In this paper, firstly the theoretical basis of four methods used to determine the minimum design metal temperature was introduced. Secondly, the mechanical properties of Q345R was measured by tensile test, Charpy v-notch impact test and fracture toughness test Thirdly, minimum design metal temperature curve of Q345R that determined by four methods were obtained. There are obvious difference between the curves of Q345R that determined by four methods. It can be concluded that low temperature fracture toughness of Q345R is underestimated when classifying Q345R into exemption curve A in American Society of Mechanical Engineers VIII-2 (2007).

Analysis of damaged Alumina Enhanced Thermal Barrier

The paper presents the problem of aerodynamic heating of a damaged Alumina Enhanced Thermal Barrier AETB. At the given minimum dimensions of the cover layers, the impact of damage size on the temperature increase on the skin surface was analyzed. The aim of the study was to determine the temperature curve as a function of the size of damage. In the calculations FreeFem ++ non-commercial environment was used.

Modeling analysis and optimization of temperature curve of welding furnace

Reflux welding is widely used in SMT (surface patch technology) During this production process, the quality of the product is essential to maintain the temperature and the furnace speed required by the process. The furnace temperature curve in the furnace is an important form of reaction welding process. In order to improve the process efficiency of the return furnace, the heating welding process model is established based on the Fourier heat conduction law,1 D heat conduction model and Newton cooling law and draws the furnace temperature curve model. Then, the upper boundary of the conveyor speed using the boundary analysis and multiple target planning, and further explore the research and optimization direction of subsequent process flow. At the same time, this paper examines and analyzes the modeling process and results, and effectively demonstrates the scientific nature and accuracy of the model. Finally, the paper analyzes the significance of the above model and research in chip processing.

Numerical Simulation of the Effect of Freeze–Thaw Cycles on the Durability of Concrete in a Salt Frost Environment

In order to improve the accuracy of the analysis of the impact of freeze–thaw cycle on concrete durability in a salt freezing environment, the numerical simulation of the impact of the freeze–thaw cycle on concrete durability in a salt freezing erosion environment is studied in this paper. Firstly, considering the influence of axial force and bending moment on the relationship between bending moment and curvature, a concrete fiber beam column model is established. Then, according to the joint influence of temperature field, stress field and seepage field on concrete in the process of freezing and thawing, the control differential equation of the freezing and thawing cycle is established. The freeze–thaw damage section is divided, the non-uniform distribution of freeze–thaw damage is determined, and the division of the freeze–thaw damage section is completed. According to the linear relationship between freeze–thaw damage degree, relative dynamic elastic modulus, freeze–thaw cycle times and position variables, the durability of concrete is numerically simulated, and the attenuation law of bond strength at different section depths after freeze–thaw is determined. The results show that the temperature curve simulated by the design method is consistent with the actually measured temperature curve, which can better reduce the temperature change of the inner core of the test block during freezing and thawing, and the relative dynamic elastic modulus is in good agreement with the actual value, which can prove that the method in this paper has certain practical application value. It is expected to provide some reference for solving the durability problem of concrete in a salt frost erosion environment and the optimal design of concrete structures.

Thermodynamic Mechanism of the Density and Compressibility Anomalies of Water in the Range -30<T(oC) <100

Compared to normal liquids, water exhibits a variety of anomalous thermal behaviors. This fact has been known for centuries. However, the thermodynamic mechanisms behind them have not been elucidated despite the efforts of many researchers. Under such circumstances, the author theoretically reproduced the measured values of the density-temperature curve at 1 atm for water above 0 oC. Then, the mystery of negative thermal expansion was clarified in relation to the shapes of the intermolecular interactions. In this paper, the author develops this line of work further and presents the interactions between water molecules to simultaneously reproduce the measured values of both the density-temperature curve and the isothermal compressibility-temperature curve in the range -30<100 at 1 atm. Then, the thermodynamic mechanism that produces these thermal behaviors is clarified in relation to the shapes of the interactions between molecules. Unraveling the mystery of related phenomena in relation to the shapes of the interaction between molecules has been a traditional and fundamental method in physics since the days of Newton.

Postoperative leukocytosis Witter (Surg., gyn. a. obst., 1925, 1)

Witter (Surg., Gyn. A. Obst., 1925, 1), on the basis of a study of 30 cases, comes to the conclusion that 1) postoperative leukocytosis reaches its inaximum a on the 4th hour after the operation and returns to normal on the 5th day , 2) its height is directly proportional to the duration of the operation and the degree of the surgical trauma, the other factors are not; are significant, 3) it is expressed mainly by polynucleosis, 4) its curve generally corresponds to the temperature curve, but not with complete accuracy.