NiTi-Cu Bimetallic Structure Fabrication through Wire Arc Additive Manufacturing.

This study endeavors to comprehensively explore and elucidate the seamless integration of NiTi shape memory alloys (SMAs) into multifaceted applications through the utilization of novel joining techniques. The primary focus lies in the utilization of wire arc additive manufacturing (WAAM) to deposit Nitinol (NiTi) onto Copper (Cu), thereby introducing a transformative approach for their integration into electro-mechanical systems and beyond. Through a detailed examination of the NiTi/Cu bimetallic junction, using advanced analytical techniques including SEM, XRD, and DSC analyses, this research aims to unravel the intricate complexities inherent within the interface. The SEM images and X-ray patterns obtained reveal a complex and nuanced interface characterized by a broad mixed zone comprising various constituents, including Ti(Ni,Cu)2, pure Cu, Ti2(Ni,Cu)3 precipitates, and Ni-rich NiTi precipitates. The DSC results, showcasing low-intensity broad peaks during thermal cycling, underscore the inherent challenges in demonstrating functional properties within the NiTi/Cu system. Recognizing the critical importance of an enhanced martensitic transformation, this study delves into the effects of heat treatment. Calorimetric curves post-annealing at 500 °C exhibit distinct transformation peaks, shedding light on the intricate influence of NiTi layer distribution within the junction. The optimal heat treatment parameters for NiTi/Cu junction restoration are meticulously explored and determined at 500 °C for a duration of 12 h. Furthermore, the study offers valuable insights into optimizing NiTi-Cu joints, with micro-hardness values reaching 485 HV and compressive strength scaling up to 650 MPa. These significant findings not only hold promise for diverse applications across various industries but also pave the way for further research directions and explorations into the realm of SMA integration and advanced joining methodologies.

Mechanical Properties, Microstructure, and Actuation Behavior of Wire Arc Additive Manufactured Nitinol: Titanium Bimetallic Structures.

Nitinol (NiTi) is well known for its corrosion resistance, shape memory effect, superelasticity, and biocompatibility, whereas Titanium (Ti) is well known for its high specific strength, corrosion resistance, and biocompatibility. The bimetallic joint of NiTi and Ti is required for applications that require tailored properties at different locations within the same component, as well as to increase design flexibility while reducing material costs. However, because of the formation of brittle intermetallic phases, connecting NiTi and Ti is difficult. In the present study, a systematic experimental investigation is carried out to develop NiTi-Ti bimetallic joint using wire arc additive manufacturing (WAAM) for the first time and to evaluate its microstructure, mechanical properties, martensitic transformation, and actuation behavior in the as-built condition. The defect-free joint is obtained through WAAM and microstructural studies indicate the formation of intermetallics at the NiTi-Ti interface leading to higher microhardness values (600 HV). Shape recovery behavior and phase transformation temperature were also enhanced in comparison to NiTi. An improved actuation and bending angle recovery is observed in comparison with NiTi. The present study lays the way for the use of WAAM in the construction of NiTi and Ti bimetallic structures for engineering and medicinal applications.

Bicuspid Morphology and Rapid Deployment Valve Replacement: Is This Still a Contraindication?

When using rapid deployment surgical aortic valve replacement (RD SAVR) in treating bicuspid aortic valve morphology (BAV), several challenges are faced due to annular asymmetry. The Sievers classification has been traditionally used for the description of BAV morphology. In this study, we aimed to conduct a retrospective feasibility analysis of RD SAVR in relation to the Sievers classification. From January 2014 to March 2022, 31 patients with BAV morphology (15 patients with Sievers type 0 BAV and 16 with Sievers type 1 BAV) underwent RD SAVR. Specific surgical techniques were applied depending on the BAV morphology. Comparable clinical outcomes were observed. No paravalvular leaks and no valvular re-interventions occurred in either group. CPB and cross-clamping times, as well as the prosthesis sizes used, were also not significantly different. Postoperative mean gradients were comparable in both groups. No significant distinction was found between the groups in terms of postoperative pacemaker indication, postoperative stroke, or death. Annular symmetry can be adequately restored through precise prosthesis sizing and placement according to an individual's valve morphology regardless of the Sievers classification of BAV by choosing a different landmark for the initial suture. RD SAVR seems to be a safe approach for any bicuspid morphology, with good hemodynamic results and time-saving potential in experienced hands.

Evaluation of a rapid deployment prosthesis strategy for the treatment of aortic valve endocarditis.

OBJECTIVES: The aim of this study was to evaluate the surgical outcome of patients suffering from native aortic valve (NVE) or prosthetic aortic valve endocarditis (PVE) treated with the EDWARDS INTUITY Elite rapid-deployment valve prosthesis. METHODS: Between February 2019 and June 2020, 25 patients suffering from NVE (n = 9; 36%) and PVE (n = 16; 64%) of the aortic valve received an INTUITY valve at our institution. Preoperative, operative and follow-up data were collected. RESULTS: In our cohort, the mean EuroSCORE II was 13.4%. Eleven patients (44%) received concomitant aortic root patch plasty. Four patients (16%) received coronary artery bypass graft surgery, 3 patients (12%) received mitral valve repair and 2 patients (8%) underwent replacement of the ascending aorta. The cardiopulmonary bypass and aortic cross-clamp times were 124 ± 56 and 75 ± 39 min, respectively. The mean intensive care unit stay was 5 days. The mean size of the implanted prostheses was 25 ± 2 mm and the mean prosthesis transvalvular gradient 3 months after surgery was 9 ± 4 mmHg. During follow-up, no case of recurrent endocarditis occurred, 1 patient died of multisystem organ failure which had already been present preoperatively. CONCLUSIONS: Surgery for NVE and PVE of the aortic valve may be safely performed using the EDWARDS INTUITY Elite valve system. This procedure could be well implemented in cases with extensive infection, fragile root tissue and root abscesses requiring root reconstruction. In our institution, the rapid-deployment aortic valve replacement strategy has become an important tool in the armamentarium of the surgical endocarditis treatment.

Interdisciplinary Management of the Emergency Treatment in an Atrioesophageal Fistula.

The atrioesophageal fistula is a fulminant complication of radiofrequency ablation in atrial fibrillation, with a mortality as high as 80%. Surgical approaches have been insufficiently dealt with in literature. Treating a 42-year-old male patient, we developed an interdisciplinary two-step concept: (1) resection of the affected third of the esophagus and closing of the atrial defect using cardiopulmonary bypass and cardioplegic cardiac arrest; and (2) a second surgery to restore gastrointestinal continuity after an adequate term. Our patient has fully recovered.

How Many Isomers Do Metallic Clusters Have? Case of Magnesium Clusters of up to 55 Atoms.

About 9000 structures of magnesium clusters Mgn (n = 2-13) generated via different methods were optimized at the DFT levels in order to estimate the number of all possible stable structures that can exist for the given cluster size (∼820,000 PES points were explored in total). It was found that the number of possible cluster isomers N quickly grows with a number of atoms n; however, it is significantly lower than the number of possible nonisomorphic graph structures, which can be drawn for the given n. At the DFT potential energy surface, we found only 543 local minima corresponding to the isomers of Mg2-Mg13. The number of isomers obtained in the DFT optimizations grows with n approximately as n4, whereas the N values extrapolated to the infinite generation process grow as n8. The cluster geometries obtained from the global DFT optimization were then used to adjust two empirical potentials of Gupta type (GP) and modified Sutton-Chen type (SCG3) describing the interactions between the magnesium atoms. Using these potentials, the extensive sets of structures Mg2-Mg55 (up to 30,000 clusters for each n) were optimized to obtain the dependence of the cluster isomer count on n in the continuous range of n = 2-30 and for selected n up to n = 55. It was found that the SCG3 potential, which is closer to the DFT results, gives a number of possible isomers growing as approximately n8.9, whereas GP potential results in the n4.3 dependence.

Alternate stresses and temperature variation as factors of influence of ultrasonic vibration on mechanical and functional properties of shape memory alloys.

It is known that the main factors in a variation in the shape memory alloy properties under insonation are heating of the material and alternate stresses action. In the present work the experimental study of the mechanical behaviour and functional properties of shape memory alloy under the action of alternate stresses and varying temperature was carried out. The data obtained had demonstrated that an increase in temperature of the sample resulted in a decrease or increase in deformation stress depending on the structural state of the TiNi sample. It was shown that in the case of the alloy in the martensitic state, a decrease in stress was observed, and on the other hand, in the austenitic state an increase in stress took place. It was found that action of alternate stresses led to appearance of strain jumps on the strain-temperature curves during cooling and heating the sample through the temperature range of martensitic transformation under the constant stress. The value of the strain jumps depended on the amplitude of alternate stresses and the completeness of martensitic transformation. It was shown that the heat action of ultrasonic vibration to the mechanical behaviour of shape memory alloys was due to the non-monotonic dependence of yield stress on the temperature. The force action of ultrasonic vibration to the functional properties was caused by formation of additional oriented martensite.

Geobacillus jurassicus sp. nov., a new thermophilic bacterium isolated from a high-temperature petroleum reservoir, and the validation of the Geobacillus species.

Four thermophilic, spore-forming bacterial strains, DS1(T), DS2, 46 and 49, were isolated from the high-temperature Dagang oilfield, located in China. The strains were identified by using the polyphasic taxonomy approach. These were aerobic, gram-positive, rod-shaped, moderately thermophilic (with an optimum growth temperature of 60-65 degrees C), chemoorganotrophic bacteria capable of growing on various sugars, carboxylic acids and crude oil. Two strains, DS1(T) and DS2, were capable of growing on individual saturated hydrocarbons. The G + C content of the DNA of strains DS1(T) and DS2 was 54.5 and 53.8 mol%, respectively. The phylogenetic analysis of the 16S rDNA of strains DS1(T) and DS2 showed that they form a separate cluster within the genus Geobacillus. The cellular fatty acids of the isolates were dominated by iso-15:0, iso-16:0 and iso-17:0 acids, which are the typical fatty acids of bacteria from the genus Geobacillus. The DNA-DNA hybridization study and the comparative analysis of the morphological and chemotaxonomic characteristics of strains DS1(T) and DS2 showed that they differ from the previously described Geobacillus species and belong to a new species, which was called Geobacillus jurassicus. DS1(T) (=VKM B2301(T), = DSM 15726(T)) is the type strain of this species. According to both DNA-DNA reassociation studies and 16S rDNA sequence analysis, two other strains, 46 and 49, were assigned to the species G. stearothermophilus. In this paper, we provide evidence that the new combinations G. stearothermophilus, G. thermoleovorans, G. kaustophilus, G. thermoglucosidasius and G. thermodenitrificans may be considered to be valid.

Microbiology of formation waters from the deep repository of liquid radioactive wastes Severnyi.

The presence, diversity, and geochemical activity of microorganisms in the Severnyi repository of liquid radioactive wastes were studied. Cultivable anaerobic denitrifiers, fermenters, sulfate-reducers, and methanogens were found in water samples from a depth of 162-405 m below sea level. Subsurface microorganisms produced methane from [2-(14)C]acetate and [(14)C]CO(2), formed hydrogen sulfide from Na(2) (35)SO(4), and reduced nitrate to dinitrogen in medium with acetate. The cell numbers of all studied groups of microorganisms and rates of anaerobic processes were higher in the zone of dispersion of radioactive wastes. Microbial communities present in the repository were able to utilise a wide range of organic and inorganic compounds and components of waste (acetate, nitrate, and sulfate) both aerobically and anaerobically. Bacterial production of gases may result in a local increase of the pressure in the repository and consequent discharge of wastes onto the surface. Microorganisms can indirectly decrease the mobility of radionuclides due to consumption of oxygen and production of sulfide, which favours deposition of metals. These results show the necessity of long-term microbiological and radiochemical monitoring of the repository.

Radioisotopic, culture-based, and oligonucleotide microchip analyses of thermophilic microbial communities in a continental high-temperature petroleum reservoir.

Activity measurements by radioisotopic methods and cultural and molecular approaches were used in parallel to investigate the microbial biodiversity and its physiological potential in formation waters of the Samotlor high-temperature oil reservoir (Western Siberia, Russia). Sulfate reduction with rates not exceeding 20 nmol of H(2)S liter(-1) day(-1) occurred at 60 and 80 degrees C. In upper horizons (AB, A, and B), methanogenesis (lithotrophic and/or acetoclastic) was detected only in wells in which sulfate reduction did not occur. In some of the wells from deeper (J) horizons, high-temperature sulfate reduction and methanogenesis occurred simultaneously, the rate of lithotrophic methanogenesis exceeding 80 nmol of CH(4) liter(-1) day(-1). Enrichment cultures indicated the presence of diverse physiological groups representing aerobic and anaerobic thermophiles and hyperthermophiles; fermentative organotrophs were predominant. Phylogenetic analyses of 15 isolates identified representatives of the genera Thermotoga, Thermoanaerobacter, Geobacillus, Petrotoga, Thermosipho, and Thermococcus, the latter four being represented by new species. Except for Thermosipho, the isolates were members of genera recovered earlier from similar habitats. DNA obtained from three samples was hybridized with a set of oligonucleotide probes targeting selected microbial groups encompassing key genera of thermophilic bacteria and archaea. Oligonucleotide microchip analyses confirmed the cultural data but also revealed the presence of several groups of microorganisms that escaped cultivation, among them representatives of the Aquificales/Desulfurobacterium-Thermovibrio cluster and of the genera Desulfurococcus and Thermus, up to now unknown in this habitat. The unexpected presence of these organisms suggests that their distribution may be much wider than suspected.

Local chemotherapy with cisplatin-depot for glioblastoma multiforme.

Glioblastoma multiforme (GBM) makes up as many as 30% of all primary brain tumors. Despite the employment of multimodal antitumor treatment, the overall survival is less than one year. Between 06/01/1998 and 06/01/2000 17 patients (Group A) with GBM (11 males, 6 females; median age 54.3 years) were administered local chemotherapy with cisplatin incorporated into biodegradable 6-carboxylcellulose polymer (cisplatin-depot (CDDP-D)). After the subtotal removal of GBM, twenty 1.5 x 1.5 cm polymer plates with a total area of 45 cm2 (the density of cisplatin immobilization on 6-carboxylcellulose being 1 mg/cm2, a total cisplatin dose of 45 mg) were implanted into the tumor bed. Group B (21 patients with GBM; 11 males, 10 females; median age 53.2 years) was control: the subtotal tumor ablation without CDDP-D implantation. Two to three weeks after the surgery all the patients of Groups A and B started a course of radiation therapy. A total dose of cranial irradiation was 20 Gy (1 fraction/day, 5 days/week; a daily dose of 2 Gy) followed by a boost tumor bed irradiation (1 fraction/day, 5 days/week; a daily dose of 2 Gy) up to the conventional dose of 60 Gy. Survival data for the patients were processed using the Kaplan-Meier method and analyzed by logrank test. All the patients of Group A tolerated surgical ablation of the brain tumor without side effects (brain edema, seizures, etc.). No patient of Group A had a reduction in blood cell counts during six weeks that would indicate systemic exposure to cisplatin. Blood chemistry and urinalysis did not show evidence of renal injury. No side effects of radiotherapy were registered in Group B either, regarding both the psychoneurological status of the patients and the basic values of homeostasis. Karnofsky performance scale (KPS) score of Group A and Group B patients demonstrated no significant differences before and after the surgery. The median overall survivals for patients of Group A and Group B were 427.5 and 211.0 days respectively (p = 0.00001; overall logrank test). Conclusion. Local chemotherapy of GBM with CDDP-D followed by irradiation is well tolerated and effective.