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Cavitation Inception in Immersed Jet Shear Flows
Cavitation inception occurring in immersed jets was investigated in a purpose-built mechanical flow rig. The rig utilized custom-built cylindrical and conical nozzles to direct high-velocity jets of variable concentration n-octane-hexadecane mixtures into a fused silica optically accessible receiver. The fluid pressure upstream and down-stream of the nozzles were manually controlled. The study employed a variety of acrylic and metal nozzles. The results show that the critical upstream pressure to downstream pressure ratio for incipient cavitation decreases with increasing n-octane concentration for the cylindrical nozzles, and increases with increasing n-octane concentration for the conical nozzle
Sensitive VLBI Studies of the OH Megamaser Emission from IRAS 17208-0014
We present phase-referenced VLBI results on the radio continuum and the OH 18
cm megamaser emission from the Ultra-Luminous Infrared Galaxy, IRAS
17208--0014. The observations were carried out at 1599 MHz using the Very Long
Baseline Array, the phased VLA, and the Green Bank Telescope. The highest
resolution radio continuum results show several compact sources with brightness
temperatures on the order of K. These sources are more likely to be
clustered supernova remnants and/or luminous radio supernovae. However, the
agreement between the number of observed and expected compact sources above the
5 level supports the possibility that each one of the compact sources
could be dominated by a recently detonated luminous radio supernova. The
continuum results suggest that there is no radio-loud AGN in the nuclear region
of this galaxy. The OH 18 cm megamaser emission in IRAS 17208--0014 is detected
at various angular resolutions. It has an extent of pc, and is
mostly localized in two regions separated by 61 pc. The structure and dynamics
of the maser emission seem to be consistent with a clumpy, rotating, ring-like
geometry, with the two dominant maser regions marking the tangential points of
the proposed rotating-ring distribution. Assuming Keplerian motion for the
rotating maser ring, the enclosed dynamical mass and the mass density within a
radius of 30.5 pc, are about {}, and
, respectively.Comment: 8 pages, 5 figures. ApJ Accepte
Robust Myco-Composites as a Platform for Versatile Hybrid-Living Structural Materials
Fungal mycelium, a living network of filamentous threads, thrives on
lignocellulosic waste and exhibits rapid growth, hydrophobicity, and intrinsic
regeneration, offering a potential means to create next-generation sustainable
and functional composites. However, existing hybrid-living mycelium composites
(myco-composites) are tremendously constrained by conventional mold-based
manufacturing processes, which are only compatible with simple geometries and
coarse biomass substrates that enable gas exchange. Here we introduce a class
of structural myco-composites manufactured with a novel platform that harnesses
high-resolution biocomposite additive manufacturing and robust mycelium
colonization with indirect inoculation. We leverage principles of hierarchical
composite design and selective nutritional provision to create a robust
myco-composite that is scalable, tunable, and compatible with complex
geometries. To illustrate the versatility of this platform, we characterize the
impact of mycelium colonization on mechanical and surface properties of the
composite, finding that it yields the strongest mycelium composite reported to
date, and demonstrate fabrication of unique foldable bio-welded containers and
flexible mycelium textiles. This study bridges the gap between biocomposite and
hybrid-living materials research, opening the door to advanced structural
mycelium applications and demonstrating a novel platform for development of
diverse hybrid-living materials
Thermoelastic Damping in Micro- and Nano-Mechanical Systems
The importance of thermoelastic damping as a fundamental dissipation
mechanism for small-scale mechanical resonators is evaluated in light of recent
efforts to design high-Q micrometer- and nanometer-scale electro-mechanical
systems (MEMS and NEMS). The equations of linear thermoelasticity are used to
give a simple derivation for thermoelastic damping of small flexural vibrations
in thin beams. It is shown that Zener's well-known approximation by a
Lorentzian with a single thermal relaxation time slightly deviates from the
exact expression.Comment: 10 pages. Submitted to Phys. Rev.
An evaluation of Bradfordizing effects
The purpose of this paper is to apply and evaluate the bibliometric method Bradfordizing for information retrieval (IR) experiments. Bradfordizing is used for generating core document sets for subject-specific questions and to reorder result sets from distributed searches. The method will be applied and tested in a controlled scenario of scientific literature databases from social and political sciences, economics, psychology and medical science (SOLIS, SoLit, USB Köln Opac, CSA Sociological Abstracts, World Affairs Online, Psyndex and Medline) and 164 standardized topics. An evaluation of the method and its effects is carried out in two laboratory-based information retrieval experiments (CLEF and KoMoHe) using a controlled document corpus and human relevance assessments. The results show that Bradfordizing is a very robust method for re-ranking the main document types (journal articles and monographs) in todayâs digital libraries (DL). The IR tests show that relevance distributions after re-ranking improve at a significant level if articles in the core are compared with articles in the succeeding zones. The items in the core are significantly more often assessed as relevant, than items in zone 2 (z2) or zone 3 (z3). The improvements between the zones are statistically significant based on the Wilcoxon signed-rank test and the paired T-Test
The electric double layer has a life of its own
Using molecular dynamics simulations with recently developed importance
sampling methods, we show that the differential capacitance of a model ionic
liquid based double-layer capacitor exhibits an anomalous dependence on the
applied electrical potential. Such behavior is qualitatively incompatible with
standard mean-field theories of the electrical double layer, but is consistent
with observations made in experiment. The anomalous response results from
structural changes induced in the interfacial region of the ionic liquid as it
develops a charge density to screen the charge induced on the electrode
surface. These structural changes are strongly influenced by the out-of-plane
layering of the electrolyte and are multifaceted, including an abrupt local
ordering of the ions adsorbed in the plane of the electrode surface,
reorientation of molecular ions, and the spontaneous exchange of ions between
different layers of the electrolyte close to the electrode surface. The local
ordering exhibits signatures of a first-order phase transition, which would
indicate a singular charge-density transition in a macroscopic limit
A field study of team working in a new human supervisory control system
This paper presents a case study of an investigation into team behaviour in an energy distribution company. The main aim was to investigate the impact of major changes in the company on system performance, comprising human and technical elements. A socio-technical systems approach was adopted. There were main differences between the teams investigated in the study: the time of year each control room was studied (i.e. summer or winter),the stage of development each team was in (i.e. 10 months), and the team structure (i.e. hierarchical or heterarchical). In all other respects the control rooms were the same: employing the same technology and within the same organization. The main findings were: the teams studied in the winter months were engaged in more `planningâ and `awarenessâ type of activities than those studies in the summer months. Newer teams seem to be engaged in more sharing of information than older teams, which maybe indicative of the development process. One of the hierarchical teams was engaged in more `system-drivenâ activities than the heterarchical team studied at the same time of year. Finally, in general, the heterarchical team perceived a greater degree of team working culture than its hierarchical counterparts. This applied research project confirms findings from laboratory research and emphasizes the importance of involving ergonomics in the design of team working in human supervisory control
The Effect of 53 micron IR Radiation on 18 cm OH Megamaser Emission
OH megamasers (OHMs) emit primarily in the main lines at 1667 and 1665 MHz,
and differ from their Galactic counterparts due to their immense luminosities,
large linewidths and 1667/1665 MHz flux ratios, which are always greater than
one. We find that these maser properties result from strong 53 micron radiative
pumping combined with line overlap effects caused by turbulent linewidths of
about 20 km/s; pumping calculations that do not include line overlap are
unreliable. A minimum dust temperature of about 45 K is needed for inversion,
and maximum maser efficiency occurs for dust temperatures in the range 80 - 140
K. We find that warmer dust can support inversion at lower IR luminosities, in
agreement with observations. Our results are in good agreement with a clumpy
model of OHMs, with clouds sizes about 1 pc and OH column densities about 5e16
cm^2, that is able to explain both the diffuse and compact emission observed
for OHMs. We suggest that all OH main line masers may be pumped by far-IR
radiation, with the major differences between OHMs and Galactic OH masers
caused by differences in linewidth produced by line overlap. Small Galactic
maser linewidths tend to produce stronger 1665 MHz emission. The large OHM
linewidths lead to inverted ground state transitions having approximately the
same excitation temperature, producing 1667/1665 MHz flux ratios greater than
one and weak satellite line emission. Finally, the small observed ratio of
pumping radiation to dense molecular gas, as traced by HCN and HCO, is a
possible reason for the lack of OH megamaser emission in NGC 6240.Comment: Accepted to ApJ, 26 pages including 1 table and 7 figure
Shocked molecular gas towards the SNR G359.1-0.5 and the Snake
We have found a bar of shocked molecular hydrogen (H2) towards the OH(1720
MHz) maser located at the projected intersection of supernova remnant (SNR)
G359.1-0.5 and the nonthermal radio filament, known as the Snake. The H2 bar is
well aligned with the SNR shell and almost perpendicular to the Snake. The
OH(1720 MHz) maser is located inside the sharp western edge of the H2 emission,
which is consistent with the scenario in which the SNR drives a shock into a
molecular cloud at that location. The spectral-line profiles of 12CO, HCO+ and
CS towards the maser show broad-line absorption, which is absent in the 13CO
spectra and most probably originates from the pre-shock gas. A density gradient
is present across the region and is consistent with the passage of the SNR
shock while the H2 filament is located at the boundary between the pre--shocked
and post-shock regions.Comment: 8 pages, 12 figures, accepted by the MNRAS, typos fixe
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