24 research outputs found
The use of a ns-pulsed, high repetition rate green laser for SLM of 99.9% pure Cu
No full textThe most common laser type used in selective laser melting (SLM) machines is continuous fiber laser emitting at 1 m. The low optical absorptivity of Cu to ~1 m wavelength renders pure Cu a highly demanding material for SLM . The low optical absorptivity along with high thermal conductivity causes unstable processing conditions when standard SLM machine are used with pure Cu. Conversely, Cu has a much higher optical absorptivity at the green wavelength. Until recently, high power green lasers have not been available for material processing. This work investigates the use of a novel ns-pulsed fiber laser operating at the second harmonic (532 nm) for SLM of 99.9% pure Cu powder. In particular, the laser source operates at 30 MHz repetition rate providing ns regime and up to 110 W average power. The green laser is implemented to a bespoke open SLM platform. Results show that cubic specimens with densities >99.5% could be achieved
Limits and solutions in processing pure Cu via selective laser melting using a high-power single-mode fiber laser
No full textThe demand for additive manufacturing (AM) of Cu and its alloys shows an increased trend from the energy and heat transfer–related applications. Selective laser melting (SLM) is amongst the key AM processes for metals, providing high geometrical accuracy and design flexibility. The technology is most commonly employed using high-brilliance fibre lasers operating at 1 μm. However, the elevated reflectivity of Cu at this wavelength, combined with its high thermal conductivity, is the cause for a highly unstable process, whereby pore-free products are difficult to obtain. Accordingly, the present work explores the limitations in processing pure Cu powders with a 1-kW single-mode fibre laser providing solutions and different strategies for improving part quality. The process parameters were studied for single and multi-pass melting strategies. The power level requirements, as well as the build plate material, are assessed through an analytical model. The results demonstrate that a correct sequence of multi-pass strategies can improve the part density up to 99.1% ± 0.2% with an industrially acceptable build rate of 12.6 cm3/h
Selective Laser Melting di componenti in rame puro per applicazioni ad alta conducibilità termica ed elettrica
No full textSelective laser melting of pure Cu with a 1 kW single mode fiber laser
No full textComplex geometries and fine critical features enabled by the powder bed fusion technologies are highly appealing for heat exchanger manufacturing. Copper is the main metal of choice for such applications. However, its processability using Selective Laser Melting (SLM) systems is limited by its high reflectivity at 1 μm, the emission wavelength of the laser sources commonly employed. Furthermore, the high conductivity of the pure copper, desirable for the final use of the products, causes instability and difficulties in the powder bed solidification. Resultantly, high density components are difficult to obtain. In this work, a 1 kW single mode fiber laser is used to process pure Cu powder with 99.9% purity. The high power is required to overcome the low efficiency of the process due to the high reflectivity. A prototype SLM machine is employed allowing for a flexible manipulation of the process parameters. The densification phenomenon is discussed as well as the causes that lead to porosity
Arteriopatia occlusiva perlferica: Ruolo dell'angio-RM
No full textPurpose. Magnetic resonance angiography (MRA) has recently become instrumental in the diagnosis of arterial disease in various body districts and is gaining an increasingly important role in the study of peripheral vascularisation. The aim of our study was to evaluate the reliability of MRA using digital subtraction angiography (DSA) as the reference standard. Materials and methods. Between November 2003 and August 2004, 30 patients with known peripheral arterial disease were studied by MRA and DSA. MRA was performed with a Philips Intera 1.5 T, with acquisitions from the coeliac trunk to the feet. For acquisitions of the feet and ankles we used unenhanced time-of-flight (TOF) sequences with a head coil. The angiographic sequence was acquired in three volumes of 40-45 cm after administration of paramagnetic contrast material. Results. In the patients with peripheral arterial disease, the technique provided a precise evaluation of the stenosis (mild, moderate, severe) or obstruction of the peripheral district as well as the detection of other diseases, such as stenosis of the renal arteries or aneurysms. Conclusions. Total-body three-dimensional (3D) MRA allows a fast, safe, and accurate assessment of the arterial system in patients with arteriosclerosis and can be considered an alternative to DSA in the management of patients with steno-obstructive disease of the peripheral arteries
High speed videography of gap bridging with beam oscillation and wire feeding during the laser welding of stainless steel and aluminum alloys
No full textLaser beam welding is known for its quality and speed. Given its susceptibility to gaps, the technology is applied in the industrial field with hard automation and dedicated fixtures rather than small-batch production. The latter cannot always guarantee the strict conditions on the fit-up of joints, especially with complex geometries. Gap-bridging techniques may be exploited to overcome these inaccuracies. The present work investigates the simultaneous use of low frequency circular beam oscillation and wire feeding as means to produce a continuous weld seam in the presence of constant air gaps. Lap joint welding of 2 mm-thick AISI301LN and butt joint welding of 3 mm-thick AW6005A-T6 alloy were conducted with gaps up to 1mm. High-speed imaging at 10kHz provided an insight in the dynamics of the oscillating weld pool and spatter formation. Optical inspection and metallographic analyses were used to verify the gap-bridging capability as well as the resulting seam quality
Correction to: Human behavior and Homo-mammal interactions at the first European peopling: new evidence from the Pirro Nord site (Apricena, Southern Italy) (The Science of Nature, (2019), 106, 5-6, (16), 10.1007/s00114-019-1610-4)
No full textIn the original publication of this article, one of the author names was incorrectly captured. The first name should be Razika, then family name should be Chelli–Cheheb
Impact of age and gender on glioblastoma onset, progression, and management
No full textGlioblastoma (GBM) is the most common primary malignant brain tumor in adults, while its frequency in pe-diatric patients is 10-15%. For this reason, age is considered one of the major risk factors for the development of GBM, as it correlates with cellular aging phenomena involving glial cells and favoring the process of tumor transformation. Gender differences have been also identified, as the incidence of GBM is higher in males than in females, coupled with a worse outcome. In this review, we analyze age-and gender-dependent differences in GBM onset, mutational landscape, clinical manifestations, and survival, according to the literature of the last 20 years, focusing on the major risk factors involved in tumor development and on the mutations and gene alter-ations most frequently found in adult vs young patients and in males vs females. We then highlight the impact of age and gender on clinical manifestations and tumor localization and their involvement in the time of diagnosis and in determining the tumor prognostic value
MAPK activation drives male and female mouse teratocarcinomas from late primordial germ cells
No full textgerm cell tumors (GCTs) are rare tumors that can develop in both sexes, peaking in adolescents. to understand the mechanisms that underlie germ cell transformation, we established a GCT mouse model carrying a germ-cell-specific BRafV600E mutation with or without heterozygous pten deletion. both male and female mice developed monolateral teratocarcinomas containing embryonal carcinoma (EC) cells that showed an aggressive phenotype and metastatic ability. germ cell transformation started in fetal gonads and progressed after birth leading to gonadal invasion. early postnatal testes showed foci of tumor transformation, whereas ovaries showed increased number of follicles, multi-ovular follicles (MOFs) and scattered metaphase I oocytes containing follicles. our results indicate that MAPK (herein referring to Erk1/2) overactivation in fetal germ cells of both sexes can expand their proliferative window leading to neoplastic transformation and metastatic behavior
Dietary Exposure to Pesticide and Veterinary Drug Residues and Their Effects on Human Fertility and Embryo Development: A Global Overview
No full textDrug residues that contaminate food and water represent a serious concern for human health. The major concerns regard the possible irrational use of these contaminants, since this might increase the amplitude of exposure. Multiple sources contribute to the overall exposure to contaminants, including agriculture, domestic use, personal, public and veterinary healthcare, increasing the possible origin of contamination. In this review, we focus on crop pesticides and veterinary drug residues because of their extensive use in modern agriculture and farming, which ensures food production and security for the ever-growing population around the world. We discuss crop pesticides and veterinary drug residues with respect to their worldwide distribution and impacts, with special attention on their harmful effects on human reproduction and embryo development, as well as their link to epigenetic alterations, leading to intergenerational and transgenerational diseases. Among the contaminants, the most commonly implicated in causing such disorders are organophosphates, glyphosate and antibiotics, with tetracyclines being the most frequently reported. This review highlights the importance of finding new management strategies for pesticides and veterinary drugs. Moreover, due to the still limited knowledge on inter- and transgenerational effects of these contaminants, we underlie the need to strengthen research in this field, so as to better clarify the specific effects of each contaminant and their long-term impact
