hydraulika-i-pneumatyka: Ultra-high vacuum

Evidence: 100 • authority: 72

Ultra-high vacuum (often spelled ultrahigh in American English, UHV) is the vacuum regime characterised by pressure lower than about 1×10−9 torrs (1×10−9 mbar; 1×10−7 Pa). UHV conditions are created by pumping the gas out of a UHV chamber, and in some cases by cooling the chamber to cryogenic temperatures. In general, there are two regimes of gas flow, laminar and free molecular, defined by whether the dominant interactions are particle-particle (laminar) or particle-chamber (molecular). At UHV pressures the mean free path of a gas molecule is greater than approximately 40 km, so the gas is in free molecular flow, and gas molecules will collide with the chamber walls many times before colli…

Evidence: 42 • authority: 88

Mean Free Path of Gas Molecules in Organic Nanochannels Using Molecular Simulations. Summary A computational method using molecular–simulation data is introduced to estimate the average mean–free–path length of multicomponent hydrocarbon molecules in an organic nanochannel. Grand–canonical Monte Carlo (MC) simulation is used first to construct the equilibrium distribution of the gas molecules in the channel. These results show that the smaller the channel is, the denser the gas mixture becomes because of nanoconfinement effects. Capillary condensation occurs in the smaller channels. The fluid composition inside a channel becomes progressively heavier when the bulk–fluid pressure outside the…

Evidence: 26 • authority: 80

The mean free time and the mean free path: exact expressions for an (approximately) ideal gas

Evidence: 26 • authority: 72

A vacuum (pl.: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective vacuus (neuter vacuum) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often discuss ideal test results that would occur in a perfect vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is considerably lower than atmospheric pressure. The Latin term in vacuo is us…

Evidence: 21 • authority: 80

Monte Carlo studies of free molecular gas flow through various vacuum structures

Evidence: 21 • authority: 92

Vibrational energy transfer in collisions of molecules with metal surfaces.. The Born-Oppenheimer approximation (BOA), which serves as the basis for our understanding of chemical bonding, reactivity and dynamics, is routinely violated for vibrationally inelastic scattering of molecules at metal surfaces. The title-field therefore represents a fascinating challenge to our conventional wisdom calling for new concepts that involve explicit electron dynamics occurring in concert with nuclear motion. Here, we review progress made in this field over the last decade, which has witnessed dramatic advances in experimental methods, thereby providing a much more extensive set of diverse observations t…

Evidence: 21 • authority: 92

Modulating pressure in the Orbitrap improves sensitivity and mass resolution in charge detection mass spectrometry.. Native mass spectrometry has become a key method for studying macromolecular assemblies, providing insights into structures, stoichiometries, and binding interactions. A key aspect for the transmission of electrospray-generated bioparticles into the mass analyzer is the use of gas for collisional cooling and ion desolvation. However, in Orbitrap-based mass spectrometry, the elevated pressure may negatively affect ions, as collisions with background gas can destabilize ion trajectories, potentially leading to incorrect mass determination. These effects are amplified when the p…

Evidence: — • authority: 80

AN ESTIMATE OF THE ABSORPTION MEAN FREE PATH FOR A PHOTON IN A GAS

Evidence: — • authority: 72

Free molecular flow describes the fluid dynamics of gas where the mean free path of the molecules is larger than the size of the chamber or of the object under test. For tubes/objects of the size of several cm, this means pressures well below 10−3 mbar. This is also called the regime of high vacuum, or even ultra-high vacuum. This is opposed to viscous flow encountered at higher pressures. The presence of free molecular flow can be calculated, at least in estimation, with the Knudsen number (Kn). If Kn > 10, the system is in free molecular flow, also known as Knudsen flow. Knudsen flow has been defined as the transitional range between viscous flow and molecular flow, which is significant i…

Evidence: — • authority: 72

The atmosphere of Earth consists of a layer of mixed gas (commonly referred to as air) that is retained by gravity, surrounding the Earth's surface. It contains variable quantities of suspended aerosols and particulates that create weather features such as clouds and hazes. The atmosphere serves as a protective buffer between the Earth's surface and outer space. It shields the surface from most meteoroids and ultraviolet solar radiation, reduces diurnal temperature variation – the temperature extremes between day and night – and keeps it warm through heat retention via the greenhouse effect. The atmosphere redistributes heat and moisture among different regions via air currents, and provide…