Topology Optimization of a Single-Point Diamond-Turning Fixture for a Deployable Primary Mirror Telescope

CubeSats, known for their compact size and cost effectiveness, have gained significant popularity. However, their limited size imposes restrictions on the optical aperture and, consequently, the Ground Resolution Distance in Earth Observation missions. To overcome this limitation, the concept of deployable optical payloads with segmented primary mirrors which can unfold like petals has emerged, enabling larger synthetic apertures and enhanced spatial resolution. This study explores the potential benefits of leveraging Additive Manufacturing (AM) and Topology Optimization (TO) in the realm of ultra-precision machining, specifically single-point diamond machining. The goal is to reduce fixture weight while improving stiffness to minimize deformations caused by rotational and cutting forces which compromise optical performance. Through Finite Element Analysis, this research compares conventionally machined fixtures with those produced using AM and TO techniques. The results reveal that concept designs created via TO can achieve a remarkable 68% reduction in weight. This reduction makes the assembly, including the machining fixture and 12 U deployable segments, manageable by a single operator without the need for specialized lifting equipment. Moreover, these innovative designs lead to substantial reductions of up to 86% and 51% in deformation induced by rotational and cutting forces, respectively

Experimental and numerical study of the cold crucible melting process

The cold crucible, or induction skull melting process as is otherwise known, has the potential to produce high purity melts of a range of difficult to melt materials, including Ti–Al and Ti6Al4V alloys for Aerospace, Ti–Ta and other biocompatible materials for surgical implants, silicon for photovoltaic and electronic applications, etc. A water cooled AC coil surrounds the crucible causing induction currents to melt the alloy and partially suspend it against gravity away from water-cooled surfaces. Strong stirring takes place in the melt due to the induced electromagnetic Lorentz forces and very high temperatures are attainable under the right conditions (i.e., provided contact with water cooled walls is minimised). In a joint numerical and experimental research programme, various aspects of the design and operation of this process are investigated to increase our understanding of the physical mechanisms involved and to maximise process efficiency. A combination of FV and Spectral CFD techniques are used at Greenwich to tackle this problem numerically, with the experimental work taking place at Birmingham University. Results of this study, presented here, highlight the influence of turbulence and free surface behaviour on attained superheat and also discuss coil design variations and dual frequency options that may lead to winning crucible designs

Estudio de la variación de los perfiles de densidad electrónica en la región-D nocturna

Un coeficiente de adhesión efectivo β eff ha sido definido por los autores en trabajos anteriores. En esta comunicación se utiliza el mismo para investigar los efectos de las concentraciones de alótropos del oxígeno y de los coeficientes de recombinación ion-electrón a ion-ion, sobre los perfiles de densidad electrónica en la región-D nocturna. Se encuentra que dichos perfiles son sensibles a las variaciones con la altura del oxígeno atómico e insensibles al ozono. De los coeficientes de recombinación el único que influye en la concentración de electrones es el que responde al proceso de recombinación ion-electrón.An effective attachment coefficient β eff was defined by the authors in previous works. In this one it is used to analyze theoretically the effect of the concentration of oxygen allotropes and of ion-electron and ion-ion recombination coefficients on electron density profiles in the nighttime D-region. It is found that these profiles are sensitive to variations with height of atomic oxygen and insensitive to changes of ozone. Only the ion-electron recombination coefficient modified the electron concentrations.Asociación Argentina de Geofísicos y Geodesta

Las anomalías nocturnas de fase en MRP y el oxigeno atómico en la mesosfera - Parte I: datos experimentales

Se han analizado los registros de muy baja frecuencia (MBF) recibidos en Tucumán entre 1973 y 1976, buscando anomalías nocturnas de fase (ANF) del tipo observado por Chilton y Radicella en el mismo circuito transecuatorial en 1963-1964, encontrándose un total de 8 noches que presentan dichas anomalías de manera bien definida. Utilizando la teoría de guía de ondas de Wait y el modelo de concentración electrónica obtenido por dos de los autores (R. y R.) se ha calculado la evolución de la altura de la guía de ondas durante las anomalías como así también los cambios de gradiente de conductividad en la región de reflexión. Los resultados muestran que la base de la capa D nocturna ha descendido hasta 12 Km durante la anomalía más pronunciada.Tucumán VLF records for the 1973-1976 period have been analjr zed, looking for nighttime phase anomalies (NPA) of the type observed by Chilton and Radicella for the same transequatorial propa gation path in 1963-1964. Eight NPA have been found. The height and conductivity gradient variations of the waveguide during the NPA have been computed, using the Wait’s waveguide theory and the electron concentration model obtained by two of the authors (R, and R.). The results show that the base of the D region has descended up to 12 Km dúring the largest anomaly.Asociación Argentina de Geofísicos y Geodesta

Modeling the break-up of nano-particle clusters in aluminum- and magnesium-based metal matrix nano-composites

Aluminum- and magnesium-based metal matrix nano-composites with ceramic nano-reinforcements promise low weight with high durability and superior strength, desirable properties in aerospace, automobile, and other applications. However, nano-particle agglomerations lead to adverse effects on final properties: large-size clusters no longer act as dislocation anchors, but instead become defects; the resulting particle distribution will be uneven, leading to inconsistent properties. To prevent agglomeration and to break-up clusters, ultrasonic processing is used via an immersed sonotrode, or alternatively via electromagnetic vibration. A study of the interaction forces holding the nano-particles together shows that the choice of adhesion model significantly affects estimates of break-up force and that simple Stokes drag due to stirring is insufficient to break-up the clusters. The complex interaction of flow and co-joint particles under a high frequency external field (ultrasonic, electromagnetic) is addressed in detail using a discrete-element method code to demonstrate the effect of these fields on de-agglomeration

Association between a rare SNP in the second intron of human Agouti related protein gene and increased BMI

<p>Abstract</p> <p>Background</p> <p>The agouti related protein (AGRP) is an endogenous antagonist of the melanocortin 4 receptor and is one of the most potent orexigenic factors. The aim of the present study was to assess the genetic variability of <it>AGRP </it>gene and investigate whether the previously reported SNP rs5030980 and the rs11575892, a SNP that so far has not been studied with respect to obesity is associated with increased body mass index (BMI).</p> <p>Methods</p> <p>We determined the complete sequence of the <it>AGRP </it>gene and upstream promoter region in 95 patients with severe obesity (BMI > 35 kg/m²). Three polymorphisms were identified: silent mutation c.123G>A (rs34123523) in the second exon, non-synonymous mutation c.199G>A (rs5030980) and c.131-42C>T (rs11575892) located in the second intron. We further screened rs11575892 in a selected group of 1135 and rs5030980 in group of 789 participants from the Genome Database of Latvian Population and Latvian State Research Program Database.</p> <p>Results</p> <p>The CT heterozygotes of rs11575892 had significantly higher mean BMI value (p = 0.027). After adjustment for age, gender and other significant non-genetic factors (presence of diseases), the BMI levels remained significantly higher in carriers of the rs11575892 T allele (p = 0.001). The adjusted mean BMI value of CC genotype was 27.92 ± 1.01 kg/m²(mean, SE) as compared to 30.97 ± 1.03 kg/m²for the CT genotype. No association was found between rs5030980 and BMI.</p> <p>Conclusion</p> <p>This study presents an association of rare allele of <it>AGRP </it>polymorphism in heterozygous state with increased BMI. The possible functional effects of this polymorphism are unclear but may relate to splicing defects.</p

Crack determination from boundary measurements—Reconstruction using experimental data

In this work we assess the effectiveness of Electrical Impedance Tomography for determining the presence and the location of an interior crack from boundary measurements. Electrical Impedance Tomography uses boundary voltages and currents to image the interior of a region. We collect the data needed for this nondestructive evaluation technique by laboratory experiments and apply two numerical inversion algorithms to the data. Our experiments show that the data collected are sufficient to give good estimates of crack locations and crack sizes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45002/1/10921_2004_Article_BF00567084.pd