6,055 research outputs found
Theoretical relation between water flow rate in a vertical fracture and rock temperature in the surrounding massif
A steady-state analytical solution is given describing the temperature
distribution in a homogeneous massif perturbed by cold water flow through a
discrete vertical fracture. A relation is derived to express the flow rate in
the fracture as a function of the temperature measured in the surrounding rock.
These mathematical results can be useful for tunnel drilling as it approaches a
vertical cold water bearing structure that induces a thermal anomaly in the
surrounding massif. During the tunnel drilling, by monitoring this anomaly
along the tunnel axis one can quantify the flow rate in the discontinuity ahead
before intersecting the fracture. The cases of the Simplon, Mont Blanc and
Gotthard tunnels (Alps) are handled with this approach which shows very good
agreement between observed temperatures and the theoretical trend. The flow
rates before drilling of the tunnel predicted with the theoretical solution are
similar in the Mont Blanc and Simplon cases, as well as the flow rates observed
during the drilling. However, the absence of information on hydraulic gradients
(before and during drilling) and on fracture specific storage prevents direct
predictions of discharge rates in the tunnel
Hummingbird: A Flexible and Lightweight Inter-Domain Bandwidth-Reservation System
The current Internet lacks a bandwidth-reservation infrastructure that
enables fine-grained inter-domain reservations for end hosts. This is hindering
the provisioning of quality-of-service guarantees for real-time applications
like video calls and gaming, cloud-based systems, financial transactions,
telesurgery, and other remote applications that benefit from reliable
communication. This paper introduces Hummingbird, a novel lightweight
inter-domain bandwidth-reservation system that addresses several shortcomings
of previous designs.
Hummingbird supports flexible and composable reservations and enables
end-to-end guarantees without requiring autonomous systems to manage
reservations for their endhosts. Previous systems tied reservations to
autonomous-system numbers or network addresses, which limits the flexibility of
reservations. In contrast, our system decouples reservations from network
identities and, as a result, the control plane from the data plane. This design
choice facilitates multiple co-existing control-plane mechanisms and enables
innovative approaches, such as a control plane based on blockchain smart
contracts that offers tradeable bandwidth-reservation assets and end-to-end
guarantees. The data-plane design ensures simplicity for efficient processing
on border routers, which streamlines implementation, deployment, and traffic
policing while maintaining robust security properties.Comment: 14 pages, 7 figure
Mechanism of Cyclopropanation Reactions Mediated by (5,10,15,20-Tetra-p-tolylporphyrinato)osmium(II) Complexes
Catalytic systems derived from [Os(TTP)]2 or Fe(TTP) (TTP = 5,10,15,20-tetra-p-tolylporphyrinato) are extremely efficient at converting styrenes and diazo reagents to cyclopropanes in high yields and high stereoselectivity. A number of mechanistic studies have been undertaken to elucidate the catalytic pathway. A mono(carbene) complex, (TTP)OsCHCO2Et, has been isolated but is not the catalytically active species. An electron-withdrawing ligand trans to the carbene in (TTP)OsCHCO2Et activates the carbon fragment toward transfer to an olefin. Labeling studies with (TTP)OsCHX and N2CHY and substrate reactivity profiles are consistent with a trans-osmium(II) bis(carbene) species as the active catalyst
Physico-chemical modifications of the interactions between hemp fibres and a lime mineral matrix: impacts on mechanical properties of mortars
International audienceIn order to understand the physico-chemical mechanisms governing interactions between hemp fibres and a lime-based mineral matrix, the consequences of various chemical treatments onto hemp fibres characteristics were measured using scanning electron microscopy, thermal analysis, X-ray diffraction and FTIR spectroscopy. Secondly, effects of these treatments on the mechanical properties of lime mortars incorporating the chemically modified fibres were evaluated using 3 point bending tests. NaOH and EDTA treatments increase the crystallinity index of hemp fibres and increase the experimental rigidity of lime/natural fibres mortars. Treatments with polyethylene imine and a saturated lime solution do not induce any significant changes onto the mechanical properties. These results show that some specific chemical treatments have an impact onto the hemp/lime interfaces quality. The elaborated composite materials exhibit a higher rigidity and an improvement of the matrix /fibre charge transfer. However, the rupture stress is only slightly modified due to a relatively low fibre volumic content (10 %)
Establishing Porcine Monocyte-Derived Macrophage and Dendritic Cell Systems for Studying the Interaction with PRRSV-1
Monocyte-derived macrophages (MoMØ) and monocyte-derived dendritic cells (MoDC) are two model systems well established in human and rodent systems that can be used to study the interaction of pathogens with host cells. Porcine reproductive and respiratory syndrome virus (PRRSV) is known to infect myeloid cells, such as macrophages (MØ) and dendritic cells (DC). Therefore, this study aimed to establish systems for the differentiation and characterization of MoMØ and MoDC for subsequent infection with PRRSV-1. M-CSF differentiated monocyte-derived macrophages (MoMØ) were stimulated with activators for classical (M1) or alternative (M2) activation. GM-CSF and IL-4 generated monocyte-derived dendritic cells (MoDC) were activated with the well established maturation cocktail containing PAMPs and cytokines. In addition, MoMØ and MoDC were treated with dexamethasone and IL-10, which are known immuno-suppressive reagents. Cells were characterized by morphology, phenotype and function and porcine MØ subsets highlighted some divergence from described human counterparts, while MoDC, appeared more similar to mouse and human DCs. The infection with PRRSV-1 strain Lena demonstrated different replication kinetics between MoMØ and MoDC and within subsets of each cell type. While MoMØ susceptibility was significantly increased by dexamethasone and IL-10 with an accompanying increase in CD163/CD169 expression, MoDC supported only a minimal replication of PRRSV These findings underline the high variability in the susceptibility of porcine myeloid cells towards PRRSV-1 infection
On the usefulness of waterborne measurement of particle velocity in geoacoustic inversion
Near-tropical subsurface ice on Mars
Near-surface perennial water ice on Mars has been previously inferred down to
latitudes of about 45{\deg} and could result from either water vapor diffusion
through the regolith under current conditions or previous ice ages
precipitations. In this paper we show that at latitudes as low as 25{\deg} in
the southern hemisphere buried water ice in the shallow (< 1 m) subsurface is
required to explain the observed surface distribution of seasonal CO2 frost on
pole facing slopes. This result shows that possible remnants of the last ice
age, as well as water that will be needed for the future exploration of Mars,
are accessible significantly closer to the equator than previously thought,
where mild conditions for both robotic and human exploration lie
Thirty Meter Telescope (TMT) Narrow Field Infrared Adaptive Optics System (NFIRAOS) real-time controller preliminary architecture
The Narrow Field Infrared Adaptive Optics System (NFIRAOS) is the first light Adaptive Optics (AO) system for the Thirty Meter Telescope (TMT). A critical component of NFIRAOS is the Real-Time Controller (RTC) subsystem which provides real-time wavefront correction by processing wavefront information to compute Deformable Mirror (DM) and Tip/Tilt Stage (TTS) commands. The National Research Council of Canada - Herzberg (NRC-H), in conjunction with TMT, has developed a preliminary design for the NFIRAOS RTC. The preliminary architecture for the RTC is comprised of several Linux-based servers. These servers are assigned various roles including: the High-Order Processing (HOP) servers, the Wavefront Corrector Controller (WCC) server, the Telemetry Engineering Display (TED) server, the Persistent Telemetry Storage (PTS) server, and additional testing and spare servers. There are up to six HOP servers that accept high-order wavefront pixels, and perform parallelized pixel processing and wavefront reconstruction to produce wavefront corrector error vectors. The WCC server performs low-order mode processing, and synchronizes and aggregates the high-order wavefront corrector error vectors from the HOP servers to generate wavefront corrector commands. The Telemetry Engineering Display (TED) server is the RTC interface to TMT and other subsystems. The TED server receives all external commands and dispatches them to the rest of the RTC servers and is responsible for aggregating several offloading and telemetry values that are reported to other subsystems within NFIRAOS and TMT. The TED server also provides the engineering GUIs and real-time displays. The Persistent Telemetry Storage (PTS) server contains fault tolerant data storage that receives and stores telemetry data, including data for Point-Spread Function Reconstruction (PSFR)
NFIRAOS First Facility AO System for the Thirty Meter Telescope
NFIRAOS, the Thirty Meter Telescope's first adaptive optics system is an
order 60x60 Multi-Conjugate AO system with two deformable mirrors. Although
most observing will use 6 laser guide stars, it also has an NGS-only mode.
Uniquely, NFIRAOS is cooled to -30 C to reduce thermal background. NFIRAOS
delivers a 2-arcminute beam to three client instruments, and relies on up to
three IR WFSs in each instrument. We present recent work including: robust
automated acquisition on these IR WFSs; trade-off studies for a common-size of
deformable mirror; real-time computing architectures; simplified designs for
high-order NGS-mode wavefront sensing; modest upgrade concepts for
high-contrast imaging.Comment: ..submitted to SPIE 9148 Astronomical Telescopes and Instrumentation
- Adaptive Optics Systems IV (2014
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