The Presence of a Single Nuchal Cord in the Third Trimester May Not Affect Tei Index in LGA Fetuses.

(1) Background: The aim of this study was to assess the RV (right ventricle) and LV (left ventricle) Tei index in large for gestational age (LGA) fetuses with a single 360-degree umbilical coil of the umbilical cord around the fetal neck identified by ultrasound in the third trimester of gestation. (2) Methods: The RV and LV Tei index for the cardiac function were measured in 297 singleton pregnancies, and we identified 25 LGA fetuses. There were 48% of LGA fetuses with a nuchal umbilical cord-LGA/NC-larger for gestational age fetuses with a nuchal cord. NC was detected with a color Doppler during a transverse scan of the fetal neck, when the umbilical cord formed a U shape. All fetuses had normal anatomy and normal uterine, placental, umbilical, intracardiac and cerebral Doppler waveforms values for their gestational age. (3) Results: The RV Tei index was significantly higher in the LGA subgroup vs. AGA (0.6 ± 0.2 vs. 0.50 ± 0.2; p value = 0.01), but in LGA fetuses with a single coil of the nuchal cord, there were not any significant changes in the Tei indexes. (4) Conclusions: The Tei index might not be impacted by the presence of the nuchal cord in LGA fetuses.

Heat Transfer Analysis of 3D Printed Wax Injection Mold Used in Investment Casting.

Investment casting is one of the precise casting methods where disposable wax patterns made in wax injection molds are used to make a casting mold. The production capacity of precision foundry is determined by the time taken for producing wax patterns, which depends on the time taken for wax solidification. Wax injection molds are usually made of aluminum or copper alloys with the use of expensive and time-consuming computer numerical control (CNC) processing, which makes low-volume production unprofitable. To reduce these costs, the authors present a heat transfer analysis of a 3D printed wax injection mold. Due to the low thermal conductivity of the photopolymer resin, the influence of different cooling channels' shapes was investigated to improve the time of the manufacturing process. Transient thermal analysis was performed using COMSOL software based on the finite element method (FEM) and included a simulation of wax injection mold cooling with cold air (-23 °C), water, and without cooling. The analysis showed that use of cooling channels in the case of photopolymer material significantly reduces the solidification time of the sample (about 10 s shorter), and that under certain conditions, it is possible to obtain better cooling than obtained with the aluminum reference wax injection mold (after approximately 25-30 s). This approach allows to reduce the production costs of low-volume castings.

Investigation of the Strength of Plastic Parts Improved with Selective Induction Heating.

The use of selective induction heating of molding surfaces allows for better filling of molding cavities and has a positive effect on the properties of molded products. This is particularly important in the production of parts that include flexible hinges, which are thin plastic layers connecting two or more parts of the product. By using hinges, it is possible to expand the use of injection molding products and their capabilities. They are widely used in the production of parts for the electrical engineering industry and for packaging Fast Moving Consumer Goods (FMCG). The use of hinges also entails specific reductions in wall thickness. Increases in the shear rate can be expected, which can lead to the degradation of polymers and deterioration of mechanical properties of materials. This paper investigates injection molded flexible hinge parts manufactured with selective induction heating to improve their properties. To verify the efficiency of reduction of material degradation due to high shear rates, open/close tests of elastic hinges were performed. The linear relation between the number of cycles the hinges can withstand, mold temperature and injection time was identified, where mold temperature was the more significant factor.

Design and Simulation Study of the Induction Heated Injection Mold with Sliders.

In order to increase the quality of the products manufactured by injection molding, RTC technology can be used to achieve higher mold temperatures. As a result, the path of the injected melt can be extended, allowing the production of parts with more complex shapes and greater length. Induction heating allows heating only selected forming surfaces of the mold which increases the speed and efficiency of the process. This paper presents the concept of a detachable inductor integrated with sliders to enable the application of this technology in an injection mold with sliders, along with the theoretical model used to perform the tests. First, the effect of the magnetic concentrator shape on the process was analyzed. This was followed by a simulation study of the influence of process parameters: heating time, frequency, and electric current. An extensive analysis of the test results of the temperature distribution on the insert allowed for the selection of parameter sets that would enable obtaining the desired surface temperature without a major increase in process time. The results of simulation studies confirm the possible applications and present the range of parameters for obtaining the optimal process.

Application of Selective Induction Heating for Improvement of Mechanical Properties of Elastic Hinges.

Injection molding is a polymer processing technology used for manufacturing parts with elastic hinges. Elastic hinges are widely used in FMCG (Fast Moving Consumer Goods) packaging (e.g., bottle closures of shampoos, sauces) and in the electrical engineering industry. Elastic hinge is a thin film that connect two regions of the injection molded part, where significant shear rates are present, which can lead to the degradation of polymers and the decrease in mechanical properties. Selective induction heating is the method that improves the flow of the polymer melt through thin regions by the local increase in mold temperature. In this study, selective induction heating was used to improve mechanical properties of elastic hinges by the reduction of material degradation due to high shear rates. To verify the change of shear rates, selective induction heating simulation and injection molding simulations were performed. The linear relation between mold temperature and maximum shear rate in the cross-section was identified and the mechanical tests showed significant differences in hinge stiffness, tensile strength and elongation at break.

The effect of nuchal umbilical cord on fetal cardiac and cerebral circulation-cross-sectional study.

OBJECTIVES: The subject of our analysis is the influence of umbilical cord collision around the fetal neck on the fetal heart function and cerebral circulation. METHODS: Our study was carried out on a group of 115 fetuses from single pregnancies with physiological course, during the 15th to 40th week of pregnancy. In our analysis, we examined the following parameters: Tei index for right ventricle, Tei index for left ventricle with Tei index components: isovolumetric contraction time, isovolumetric relaxation time, ejection time and cardiothoracic area ratio, middle cerebral artery peak systolic velocity (PS MCA), middle cerebral artery pulsatility index (PI MCA). Gestational age in our study was: 28+2±34. The study group of patients with fetal umbilical cord around neck group (fUCAN) included 38 fetuses (20 males, 18 females). The control group of patients with no fetal umbilical cord around neck group (NfUCAN) included 77 fetuses (43 males, 34 females). RESULTS: In our study, we found no significant differences in the values obtained: Tei LV in fUCAN: 0.5±0.1 vs. in NfUCAN: 0.5±0.1; p=0.42), Tei RV in fUCAN: 0.5±0.2 vs. in NfUCAN: 0.4±0.1; (p=0.2). Tricuspid valve regurgitation-TR was observed with the following frequency: fUCAN: 7/38, 18% vs. NfUCAN: 13/77, 17%; p=0.8. MCA PS in study fUCAN group was significantly higher than in NfUCAN (40.2±11.5 vs. 32.5±9.5; p=0.003), although other hemodynamic and clinical variables did not differ between the study and control groups. CONCLUSIONS: The fetal nuchal umbilical cord collision did not affect the fetal heart function expressed as Tei index, at the time of fetal heart examination (at mean gestational age 29+4 weeks). The fUCAN group presented elevated PS MCA, which was not related to other hemodynamic and clinical variables between the study and control groups.

Application of Magnetic Concentrator for Improvement in Rapid Temperature Cycling Technology.

The main method to improve the filling of the cavity by the polymer melt is to increase the mold temperature. Rapid Temperature Cycling (RTC) technologies have been used around the world for several years, improving the quality of injection molded parts with a slight extension of production time. The present work focuses on the application of induction heating technology in the injection molding process since it is the most effective and most intensively developing method of heating in modern RTC technologies. In this research, the application of the induction heating process for selected surfaces was investigated with particular emphasis on the dynamics of the process. The numerical simulations were used to study the influence of the number of coils, the distance between coils and cavity surface and the mold material was examined with and without the presence of a magnetic concentrator. According to the obtained results, several crucial conclusions were made: the efficiency of heating is directly correlated with the distance between the inductor and the mold surface, the presence of magnetic flux concentrator significantly improves the homogeneity of temperature distribution and heating efficiency, application of aluminum mold lowers the obtained surface temperature.