An Active Stress Model of Caenorhabditis Elegans Locomotion

SSRN Electronic Journal · 2026-01-01

Estimation of recovery error of blade tip timing signal with influence of non-uniformity

2025-02-12

Blade tip timing (BTT) is a special non-contact blade health monitoring technology. Lots of methods to analyze and recover BTT signal have been developed. However, the effects of signal non-uniformity on signal recovery and parameter identification have not been fully addressed. In this paper, the influence of signal non-uniformity on the parameter identification using two classical methods is studied. Simulation and experimental validation are performed to verify the proposed analysis method.

Interfacial Tension Between Miscible Liquids

2024-12-17

In this paper we study some basic problems of fluid dynamics of two incompressible miscible liquids modeled as a simple mixture in which the density of the mixture is connected to the densities of the two constituents by a linear relation in the volume fraction. Since the density of such a mixture of incompressible liquids is changed by diffusion, the expansion Δ = div u does not vanish in general. The velocity in such a mixture can be decomposed into a solenoidal and an expansion part. The expansion velocity is induced by diffusion which is proportional to the gradient of the volume fraction in a simple mixture. We find that the expansion velocity is always important where the gradients of the volume fraction are sufficiently great, most especially at early times in the mixing layer arising from the smoothing of an initial plane or spherical discontinuity of composition. Another case and place where divu = 0 may be bad approximation is in driven problems of mixing layer where gradients of composition (or volume fraction) can be maintained in a competition between convection and diffusion.

Eleven Countries, an Integrated Spacecraft: The Story of International Collaboration that Built the Orion Spacecraft and Powered the Success of the Artemis I Mission

2024-01-01

Analysis of Compressor Cascade Deviation and Surrogate Model Construction Based on Retained Lift

Journal of Thermal Science · 2024-12-13 · 1 citations

Controlled Light-Driven Levitation of Macroscopic Plates

2021-04-14

Photophoretic or light-driven levitation has been studied extensively in the context of the motion of illuminated micron-sized particles, such as dust grains in the atmosphere under sunlight [1,2], and in relation to Crooks radiometers [3]. When heated by incident light, a micron-sized particle experiences a temperature gradient that in turn results in uneven gas-surface interactions and a net propulsive force [4]. Though thoroughly investigated for micron-sized particles, this phenomenon has rarely been studied to controllably levitate macroscopic objects. We report light-driven levitation of 0.5-um thick mylar samples that have been modified by depositing a 300-nm-thick layer of carbon nanotubes (CNTs) on a single side. The CNT layer serves three key purposes: 1) It acts as a lightweight light absorber, absorbing ~ 90% of the incident light and elevating the temperature of the sample. 2) It increases the structural rigidity of the mylar film, allowing cm-scale discs with submicron thicknesses to hold their shape. 3) It creates a structured porous surface that traps impinging gas molecules, which results in an accommodation coefficient difference between the top and bottom surfaces for gas-surface interactions. Air molecules that rebound from the CNT-coated side have on average higher velocities than those departing from the opposing uncoated mylar surface. We show that the net force thus created can be used to levitate the mylar films. Moreover, we will demonstrate our ability to manipulate a light field in order to control the flight of levitating samples for extended periods of time. References: Jovanovic, O. Photophoresis—Light induced motion of particles suspended in gas. Journal of quantitative spectroscopy & radiative transfer 110, 889–901, (2009) Horvath, Photophoresis – a forgotten force ??, KONA powder and particle journal, 31, 181–199 (2014) Ketsdever, N. Gimelshein, S. Gimelshein, and N. Selden, “Radiometric phenomena: From the 19th to the 21st century”, Vacuum 86, 1644-1662 (2012). Loesche, G. Wurm, T. Jankowski, M. Kuepper, Photophoresis on particles hotter/colder than the ambient gas in the free molecular flow. J. Aerosol Sci, 97, 22–33 (2016)

Controlled Levitation Of Nanostructured Thin Films For Sun-Powered Near-Space Flight

Science Advances · 2021 · 30 citations

• Computer Science
• Aerospace engineering
• Astrobiology

Earth’s mesosphere is the least studied part of our atmosphere. The data it contains within itself can help develop more comprehensive and accurate models of the atmosphere and can help us understand our climate better. The main challenge before scientists is the inaccessibility of this region. The pressure is not high enough for aircraft and balloons and it is too high for satellites. There are remote sensing methods as well as transient rockets to collect data, though they are expensive and collect data for a few minutes at a time. In this thesis, we present photophoresis or light-driven motion as an alternative flight mechanism for long-duration access to this region.Photophoretic force has long been studied for micron-scale particles. However, to leverage photophoresis to levitate large microflyers capable of carrying useful payloads under sunlight, the structure of microflyers needs to be ultralight, with areal densities of no more than a few g/m2. Creating a large-scale structure with thicknesses that result in temperature difference and weigh only a few g/m2 is a challenge. The approach we present in this thesis is to generate photophoretic force that leverages heat transfer between gas molecules and surface molecules/structure. By altering this heat transfer on either side of a thin disc we can generate large photophoretic forces that can levitate cm-scale samples with several milligrams of payload. In this work, we propose and validate a predictive theoretical framework that accounts for conductive, convective, and radiative heat transfer and determines the temperature of illuminated thin disc microflyers as well as their lift force and payload capacity with sizes ranging from millimeters to centimeters over pressures ranging from 10 to 120 pascals. We used cheap and fast methods to fabricate cm-scale thin disc microflyers with areal density of ~ 1 g/m2 and test them in vacuum and under variable light intensity. We fabricated four generations of microflyers starting by dropcasting carbon nanotubes onto thin disc-shaped mylar films. Atomic layer deposition and laser micromachining enabled stiffer continuous and porous samples to be created as well. Moreover, we used different microfabrication techniques to improve the performance of microflyers and increase their range of operation. Lastly, we used our validated theoretical model to predict the performance of the microflyers in the upper atmosphere under natural sunlight, and we further propose different approaches that can lead to better performance and higher payload carrying capabilities.

Photophoretic Levitation of Macroscopic Nanocardboard Plates

Advanced Materials · 2020 · 31 citations

• Materials science
• Aerospace engineering
• Mechanics

Scaling down miniature rotorcraft and flapping-wing flyers to sub-centimeter dimensions is challenging due to complex electronics requirements, manufacturing limitations, and the increase in viscous damping at low Reynolds numbers. Photophoresis, or light-driven fluid flow, was previously used to levitate solid particles without any moving parts, but only with sizes of 1-20 µm. Here, architected metamaterial plates with 50 nm thickness are leveraged to realize photophoretic levitation at the millimeter to centimeter scales. Instead of creating lift through conventional rotors or wings, the nanocardboard plates levitate due to light-induced thermal transpiration through microchannels within the plates, enabled by their extremely low mass and thermal conductivity. At atmospheric pressure, the plates hover above a solid substrate at heights of ≈0.5 mm by creating an air cushion beneath the plate. Moreover, at reduced pressures (10-200 Pa), the increased speed of thermal transpiration through the plate's channels creates an air jet that enables mid-air levitation and allows the plates to carry small payloads heavier than the plates themselves. The macroscopic metamaterial structures demonstrate the potential of this new mechanism of flight to realize nanotechnology-enabled flying vehicles without any moving parts in the Earth's upper atmosphere and at the surface of other planets.

Photophoretic Levitation: Photophoretic Levitation of Macroscopic Nanocardboard Plates (Adv. Mater. 16/2020)

Advanced Materials · 2020

• Materials science
• Optics
• Nanotechnology

In article number 1906878, Igor Bargatin and co-workers demonstrate that centimeter-scale hollow plates with nanoscale thickness and microscopic channels can levitate when illuminated with light intensity comparable to natural sunlight. Light-driven thermal transpiration of air through the plate's channels creates air jets, which result in small-height hovering at atmospheric pressure and mid-air flight at reduced pressures, even allowing small payloads.

The Roles of Mercury in Intracytoplasmic Sperm Injection

Journal of Vibration Testing and System Dynamics · 2020-06-09

Intracytoplasmic sperm injection (ICSI), microinjection of a single spermatozoon into an oocyte, is a routine procedure in assisted reproduction programs. This procedure uses fine control of small bore microinjection needles and precise volume control via hydraulic syringe pumps. In many early experiments mercury is placed within the injection system because its high surface tension in the system facilitates the injection procedure. However, mercury is cytotoxic and therefore alternative fluids or approaches are needed. Here we examine the main properties of mercury and their impact on the various aspects of ICSI. We conclude that the small momentum diffusivity of mercury is the most important contributing factor that facilitates the ICSI procedures.