360 research outputs found
Thermal analysis applied to estimation of solidification kinetics of Al–Si aluminium alloys
Evaluation of solidification kinetics by thermal analysis is a useful tool for quality control of Al–Si melts before pouring provided it is rapid and highly reproducible. Series of thermal analysis records made with standard cups are presented that show good reproducibility. They are evaluated using a Newton’s like approach to get the instantaneous heat evolution and from it solidification kinetics. An alternative way of calculating the zero line is proposed which is validated by the fact that the latent heat of solidification thus evaluated is within 5% of the value calculated from thermodynamic data. Solidification kinetics was found highly reproducible provided appropriate experimental conditions were achieved: high enough casting temperature for the cup to heat up to the metal temperature well before solidification starts; and equal and homogeneous temperatures of the metal and of the cup at any time in the temperature range used for integration
Experimental and numerical investigation of the weld repair of superplastic forming dies
Issu de : AMPT 2003 - International conference on advances in materials and processing technologies, Dublin, IRELAND, July 8-11, 2003International audienceSuperplastic forming process (SPF) is an advanced process conducted at high temperature using moderate strain rates, typically used for shaping TAW sheets for aerospace applications. Thermomechanical stresses on the forming dies due to successive forming cycles may result in the earl), degradation and even fracture of SPF tools through fatigue crack propagation. To reduce cost and extend service life. dies are generally weld-repaired and subsequently re-used in the typical severe conditions of SPF. The implementation of robust, easy processing welding techniques resulting in high quality repair able to sustain cumulative thermomechanical stresses is of utmost concern to SPF parts manufacturers. The paper focuses on the development of an automated TIG technique to weld repair high nickel, high chromium heat resistant alloys based on a complementary approach including thermal instrumentation, numerical simulation using Sysweld(TM) and metallurgical investigation: this former being performed on either as-received, repaired and repaired plus damaged materials
Static kinematics for an antagonistically actuated robot based on a beam-mechanics-based model
Soft robotic structures might play a major role in
the 4th industrial revolution. Researchers have successfully
demonstrated advantages of soft robotics over traditional
robots made of rigid links and joints in several application
areas including manufacturing, healthcare and surgical
interventions. However, soft robots have limited ability to exert
higher forces when it comes to interaction with the
environment, hence, change their stiffness on demand over a
wide range. One stiffness mechanism embodies tendon-driven
and pneumatic air actuation in an antagonistic way achieving
variable stiffness values. In this paper, we apply a beammechanics-based
model to this type of soft stiffness controllable
robot. This mathematical model takes into account the various
stiffness levels of the soft robotic manipulator as well as
interaction forces with the environment at the tip of the
manipulator. The analytical model is implemented into a
robotic actuation system made of motorised linear rails with
load cells (obtaining applied forces to the tendons) and a
pressure regulator. Here, we present and analyse the
performance and limitations of our model
The false memory syndrome: Experimental studies and comparison to confabulations
a b s t r a c t False memories, or recollections that are factually incorrect but strongly believed, remain a source of confusion for both psychiatrists and neurologists. We propose model for false memories based on recent experimental investigations, particularly when analyzed in comparison to confabulations, which are the equivalent of false memories from neurological disease. Studies using the Deese/Roedinger-McDermott experimental paradigm indicate that false memories are associated with the need for complete and integrated memories, self-relevancy, imagination and wish fulfillment, familiarity, emotional facilitation, suggestibility, and sexual content. In comparison, confabulations are associated with the same factors except for emotional facilitation, suggestibility, and sexual content. Both false memories and confabulations have an abnormal sense of certainty for their recollections, and neuroanatomical findings implicate decreased activity in the ventromedial frontal lobe in this certainty. In summary, recent studies of false memories in comparison to confabulations support a model of false memories as internally-generated but suggestible and emotionally-facilitated fantasies or impulses, rather than repressed memories of real events. Furthermore, like confabulations, in order for false memories to occur there must be an attenuation of the normal, nonconscious, right frontal ''doubt tag'' regarding their certainty. Published by Elsevier Ltd
Highly dexterous 2-module soft robot for intra-organ navigation in minimally invasive surgery
Large-Scale Statistical Analysis of Defect Emission in hBN: Revealing Spectral Families and Influence of Flakes Morphology
Quantum emitters in two-dimensional layered hexagonal boron nitride are
quickly emerging as a highly promising platform for next-generation quantum
technologies. However, precise identification and control of defects are key
parameters to achieve the next step in their development. We conducted a
comprehensive study by analyzing over 10,000 photoluminescence emission lines,
revealing 11 distinct defect families within the 1.6 to 2.2 eV energy range.
This challenges hypotheses of a random energy distribution. We also reported
averaged defect parameters, including emission linewidths, spatial density,
phonon side bands, and the Debye-Waller factors. These findings provide
valuable insights to decipher the microscopic origin of emitters in hBN hosts.
We also explored the influence of hBN host morphology on defect family
formation, demonstrating its crucial impact. By tuning flake size and
arrangement we achieve selective control of defect types while maintaining high
spatial density. This offers a scalable approach to defect emission control,
diverging from costly engineering methods. It highlights the importance of
investigating flake morphological control to gain deeper insights into the
origins of defects and to expand the spectral tailoring capabilities of defects
in hBN
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Spatial patterns of dissipative polariton solitons in semiconductor microcavities
We report propagating bound microcavity polariton soliton arrays consisting of multipeak structures
either along (x) or perpendicular (y) to the direction of propagation. Soliton arrays of up to five solitons are
observed, with the number of solitons controlled by the size and power of the triggering laser pulse. The
breakup along the x direction occurs when the effective area of the trigger pulse exceeds the characteristic
soliton size determined by polariton-polariton interactions. Narrowing of soliton emission in energymomentum
space indicates phase locking between adjacent solitons, consistent with numerical modeling
which predicts stable multihump soliton solutions. In the y direction, the breakup originates from
inhomogeneity across the wave front in the transverse direction which develops into a stable array only in
the solitonic regime via phase-dependent interactions of propagating fronts
Physical Activity Status in Patients With Coronary Heart Disease: Results From the Cross-Sectional EUROASPIRE Surveys.
BACKGROUND: The study aim was to assess the physical activity levels as well as the intention to become physically active in patients with stable coronary heart disease (CHD) with a special focus on the association with their risk profile. METHODS: Analyses are based on the cross-sectional EUROASPIRE IV surveys. Information was available on 8966 patients in EUROASPIRE III and on 7998 patients in EUROASPIRE IV. Physical activity level according to patients risk profile and their medical management was assessed, the intention to become physically active was investigated and a time trend analysis was performed. RESULTS: A better cardiovascular risk profile as well as receiving physical activity advice or weight loss advice was associated with better physical activity levels. The physical activity status improved significantly over time, the proportion of patients reporting vigorous physical activity for at least 20 minutes ≥ 3 times/week increased from 14.1% to 20.2% (P < .001). Similarly, a significantly greater proportion of patients are in the maintenance stage (36.6% vs. 27.4%) and a smaller proportion in the precontemplation stage (43.2% vs. 52.3%). CONCLUSION: Although an increase was seen in the proportion of patients being adequately physical active, physical activity levels remain suboptimal in many CHD patients
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