STUDY ON THE EXTINGUISHING EFFICIENCY OF NaCl IMPREGNATED CELLULOSE TOWELS DURING SODIUM FIRES

The spatial and temporal distribution of forest fires displays a complex pattern which strongly influences the forest landscape and the neighbouring anthropogenic development. Statistical methods developed for spatio-temporal stochastic point processes can be employed to find a structure, detect over-densities and trends in forest fire risk and address towards prevention and forecasting measures. The present study considers the Portuguese mapped burnt areas official geodatabase resulting from interpreted satellite measurements, covering the period 1990–2013. The main goal is to detect whether space and time act independently or whether, conversely, neighbouring events are also closer in time, interacting to generate clusters. To this purpose, the following statistical methods were applied: (1) the geographically weighted summary statistics, to explore how the average burned area vary locally through the investigated region; (2) the bivariate K-function, to test the space–time interaction and the spatial attraction/independency between fires of different size; and (3) the space–time kernel density, allowing elaborating smoothed density surfaces and representing over-densities of large versus medium versus small fires and on north versus south region. The proposed approach successfully allowed finding and mapping spatio-temporal patterns within this large data series. Specifically, medium fires tend to aggregate around small fires, while large fires aggregate at a larger distance and longer times, indicating that the return time following these events is longer than for small and medium fires. The density maps shows that hot spots are present almost each year in the northern region, with a higher concentration in the northern areas, while the southern half of the country counts lower surface densities of fires, which are mainly concentrated in the central period (2000–2007).

Abstract. Climate, land use, and other anthropogenic and natural drivers have the potential to influence fire dynamics in many regions. To develop a mechanistic understanding of the changing role of these drivers and their impact on atmospheric composition, long-term fire records are needed that fuse information from different satellite and in situ data streams. Here we describe the fourth version of the Global Fire Emissions Database (GFED) and quantify global fire emissions patterns during 1997–2016. The modeling system, based on the Carnegie–Ames–Stanford Approach (CASA) biogeochemical model, has several modifications from the previous version and uses higher quality input datasets. Significant upgrades include (1) new burned area estimates with contributions from small fires, (2) a revised fuel consumption parameterization optimized using field observations, (3) modifications that improve the representation of fuel consumption in frequently burning landscapes, and (4) fire severity estimates that better represent continental differences in burning processes across boreal regions of North America and Eurasia. The new version has a higher spatial resolution (0.25°) and uses a different set of emission factors that separately resolves trace gas and aerosol emissions from temperate and boreal forest ecosystems. Global mean carbon emissions using the burned area dataset with small fires (GFED4s) were 2.2 × 1015 grams of carbon per year (Pg C yr−1) during 1997–2016, with a maximum in 1997 (3.0 Pg C yr−1) and minimum in 2013 (1.8 Pg C yr−1). These estimates were 11 % higher than our previous estimates (GFED3) during 1997–2011, when the two datasets overlapped. This net increase was the result of a substantial increase in burned area (37 %), mostly due to the inclusion of small fires, and a modest decrease in mean fuel consumption (−19 %) to better match estimates from field studies, primarily in savannas and grasslands. For trace gas and aerosol emissions, differences between GFED4s and GFED3 were often larger due to the use of revised emission factors. If small fire burned area was excluded (GFED4 without the s for small fires), average emissions were 1.5 Pg C yr−1. The addition of small fires had the largest impact on emissions in temperate North America, Central America, Europe, and temperate Asia. This small fire layer carries substantial uncertainties; improving these estimates will require use of new burned area products derived from high-resolution satellite imagery. Our revised dataset provides an internally consistent set of burned area and emissions that may contribute to a better understanding of multi-decadal changes in fire dynamics and their impact on the Earth system. GFED data are available from http://www.globalfiredata.org.

The effect of metal oxide layer on the nano-tribological characteristics of single chain alkanethiol (CH3(CH2) n SH) self-assembled monolayers (SAMs) on various metal surfaces (gold, silver, copper) was investigated. In order to correlate the surface structures with the tribological characteristics, various surface analysis techniques such as Scanning Probe Microscopy, X-ray Photoelectron Spectroscopy, Secondary Ion Mass Spectrometry and Spectroscopic Ellipsometry were used. Results of surface analyses showed that thiols on a metal surface were susceptible to forming multilayers if the metal surface was oxidized before the thiol assembly process. From the friction and wear tests conducted using an Atomic Force Microscope and a Lateral Force Microscope, it was found that thiols on copper oxide surface could be easily removed even under a few nano-Newton normal load. On the other hand, thiols on gold and copper fresh surfaces (the surface which was made by minimizing oxide formation) could endure up to micro-Newton level loads. Based on these findings, it could be concluded that the nano-tribological characteristics of alkanethiol SAMs on various metal surfaces were largely dependent on the oxide layer that already formed on the metal surface before the thiol adsorption process.

Direct measurement of adhesion between clean metal and tool surfaces in machining

A study of heavy metal-to-plastic friction duties and of the wear of hardened steel in the presence of polymers

1. It has been shown that the relations between wear and external electrical field strength have the character of electrocapillary curves. The mechanism of additive antiwear and antiscuff action under these conditions reduces to a change in the zero-charge point of the metal surface, i.e., to a change in the electron work function. 2. External polarization of frictional surfaces gives an antiscuff action of the external electrical field that is related to metal surface plasticization. 3. By evaluating changes in the electron work function, it has been confirmed that interaction of antiscuff additives of various chemical types with a metal surface will form surface compounds that differ in mechanical properties — plastic, with a low electron work function, when certain additives are used; brittle, with a high electron work function, when others are used.

TEM Study of the Microstructural Modifications of an Alumina-Supported Palladium Combustion Catalyst

In vacuum arc cleaning (VAC) treatment of an oxide layer on a metal surface, the oxide layer is removed evaporatively by movement of high-energy-density cathode spots on it. The action of the cathode spots not only quickly removes the oxide layer on the metal surface; it also causes a rapid temperature variation on the metal surface, which might indicate a change in surface physical features and impart new additional functions. Changes of metal surfaces that had undergone VAC treatment for the oxide layer are investigated using S45C plate. A simple model is suggested and the experiment result is analyzed theoretically.

Bonding adhesive strength for plasma spray with cathode spots of low-pressure arc after grit blasting and removal of oxide layer on metal surface

A preliminary study of combining mass spectrometric data with audio and video signals for real-time monitoring of controlled lab-scale fires

The motion of cathode spots plays a crucial important role in removing oxide layer on a metal surface by vacuum arc. In this paper, the characteristics of the motion of a single cathode spot on metal surface with oxide layer are investigated experimentally. Experiments are conducted in a detachable vacuum chamber. A hollow copper anode with a hole of $10~\text {mm} \times 10$ mm is used in order to observe the 2-D motion of the cathode spot. The motion of the cathode spot during the descaling process is photographed by a high-speed digital camera with an exposure time of $2~\mu \text{s}$ . Experimental results indicate that there are slow motion and fast motion of the cathode spot during descaling process, and the slow motion is the basic characteristic in most of the descaling time. The probability distribution of the cathode spot’s displacement and resident time, the average velocity, and the movement parameter $S^{2}/t$ are analyzed quantitatively. The results indicate that with the increase of gap distance or the decrease of oxide layer thickness, the cathode spot becomes more active.

Surface metal standards produced by ion implantation through a removable layer

A remarkable characteristic of a cathode spot of a vacuum arc is that the cathode spot moves around on the metal surface. A cathode spot can remove an oxide layer. Cathode spots of vacuum arcs have been used for cleaning metal oxide surfaces. However, the influence of an oxide layer on cathode spot movement remains unclear. As described herein, cathode spot movements and voltage fluctuation on an oxide layer surface and a metal surface were measured to determine the cathode spot movement and elucidate the existence of cathode spot on the SS400 surface with oxide layer. Experiments were performed using a SS400 cathode and a cylindrical copper anode. A high-speed video camera recorded the cathode spot movement. Then the obtained images were analyzed using plasma image processing. The cathode spot movement was generated mainly on the boundary layer, but sometimes on the processed surface. The first spot remains at the boundary when the cathode spot splits; the second spot moves on the bulk surface and reappears at a different boundary. Therefore, the cathode spot does not appear suddenly; instead it moves continuously during the splitting process. In addition, when the cathode spot exits near the oxide layer, the voltage is fluctuated because of vapor from oxide layer. Therefore, The oxide layer serves an important role for cathode spot existence because of oxide layer vaporization.

Phase changes in metal combustion

Various metal (Al, Ti, Fe, Ni, and Cu) surfaces with native oxide layers were rendered "omniphobic" by a simple thermal treatment of neat liquid trimethylsiloxy-terminated polymethylhydrosiloxanes (PMHSs) with a range of different molecular weights (MWs). Because of this treatment, the PMHS chains were covalently attached to the oxidized metal surfaces, giving 2-10 nm thick PMHS layers. The resulting surfaces were fairly smooth, liquid-like, and showed excellent dynamic omniphobicity with both low contact angle hysteresis (≲5°) and substrate tilt angles (≲8°) toward small-volume liquid drops (5 μL) with surface tensions ranging from 20.5 to 72.8 mN/m. Droplet mobility was improved overall as a result of heating the substrates to 70 °C. The reaction kinetics and final dynamic dewetting properties were found to be not dependent of the types of metals employed or MWs of PMHS, but mainly dominated by both reaction temperatures and reaction times.