Forest biological disturbance agents (BDAs) are insects, pathogens, and parasitic plants that affect tree decline, mortality, and forest ecosystems processes. BDAs are commonly thought to increase ...the likelihood and severity of fire by converting live standing trees to more flammable, dead and downed fuel. However, recent research indicates that BDAs do not necessarily increase, and can reduce, the likelihood or severity of fire. This has led to confusion regarding the role of BDAs in influencing fuels and fire in fire-prone western United States forests. Here, we review the existing literature on BDAs and their effects on fuels and fire in the western US and develop a conceptual framework to better understand the complex relationships between BDAs, fuels and fire. We ask: 1) What are the major BDA groups in western US forests that affect fuels? and 2) How do BDA-affected fuels influence fire risk and outcomes? The conceptual framework is rooted in the spatiotemporal aspects of BDA life histories, which drive forest impacts, fuel characteristics and if ignited, fire outcomes. Life histories vary among BDAs from episodic, landscape-scale outbreaks (bark beetles, defoliators), to chronic, localized disturbance effects (dwarf mistletoes, root rots). Generally, BDAs convert aboveground live biomass to dead biomass, decreasing canopy fuels and increasing surface fuels. However, the rate of conversion varies with time-since-event and among BDAs and forest types, resulting in a wide range of effects on the amount of dead fuels at any given time and place, which interacts with the structure and composition of the stand before and subsequent to BDA events. A major influence on fuels may be that BDAs have emerged as dominant agents of forest heterogeneity creation. Because BDAs play complex roles in fuels and fire heterogeneity across the western US which are further complicated by interactions with climate change, drought, and forest management (fire suppression), their impacts on fuels, fire and ecological consequences cannot be categorized simply as positive or negative but need to be evaluated within the context of BDA life histories and ecosystem dynamics.
The problems of electromagnetic compatibility associated with the presence of sinusoidal voltage distortions in a public network when connecting induction heating systems are considered. One of the ...sources of voltage harmonic emissions is the designed high-frequency induction installation for heating a graphite cylinder based on a VGT 8-50/10 power supply. The problems of low-frequency conducted interference created during the operation of the induction installation for heating the graphite cylinder at high frequencies are considered. Results of experimental studies of the sinusoidal distortion of the voltage curve in the supply network are presented. Measurements are made of the voltage total harmonic distortion factor and the
n
th harmonic component factor. The voltage and current curves at the input of the VGT-series power supply with a frequency of 10 kHz are obtained when connecting it to an inductor with a power of 12 and 20 kW. Voltage harmonics are measured and compared with the maximum standard parameters. The harmonic numbers at which the permissible voltage values are exceeded are recorded.
In order to reach the ambitious net-zero emission target by 2050, various technological solutions need to be developed to ensure efficient utilisation of energy. Commercial and residential buildings ...are a big source of greenhouse gas emissions, where efficient utilisation of energy can play a major role towards decarbonisation of the buildings sector. Heat pumps have recently emerged as an effective solution for space heating applications in buildings. Energy-efficient operation of heat pumps will make a significant contribution toward making buildings energy-efficient. In this context, heat pump control systems have a major role. Some of the existing literature on the heat pump control systems assume that various system states are available to measure. This may not always be true and/or economical to measure all the states. Moreover, the system is subject to various disturbances which cannot be directly measured. To reduce the number of sensors in heat pump control systems, an adaptive observer is developed in this paper to estimate inaccessible system states and disturbances simultaneously. An advantage of the proposed approach is that it does not require any bound on the disturbance itself, however, only assumes that the rate of change of disturbance is bounded. This is always the case in practice. In the developed method, adaptive control techniques and variable structure control techniques are combined to implement the proposed observer. In order to estimate the unknown disturbance, an augmented systems model is considered. Globally uniformly ultimately bounded property of the error dynamical systems is established by suitably designing the adaptive laws. The developed method is applied to a model of the heat dynamics of a house floor heating system connected to a ground source-based heat pump. Different disturbance signals formats and amplitudes are considered to show the effectiveness of the proposed technique. Simulation results are given to demonstrate the suitability of the proposed method.
Sleep Disturbance in Heavy Marijuana Users BOLLA, Karen I; LESAGE, Suzanne R; GAMALDO, Charlene E ...
Sleep (New York, N.Y.),
06/2008, Letnik:
31, Številka:
6
Journal Article
Recenzirano
Odprti dostop
To determine if recently abstinent, heavy marijuana (MJ) users show differences in polysomnographic (PSG) measures compared with a drug-free control group.
A group of carefully selected heavy MJ ...users were chosen for study inclusion and matched to a drug-free control group. Questionnaire data were collected prior to cessation of MJ use. PSG studies were conducted during 2 consecutive nights after discontinuation of MJ use in our core sleep laboratory.
Baltimore Maryland, General Clinical Research Center (GCRC) core sleep lab.
17 heavy MJ users discontinuing MJ use and 14 drug-free controls. Men and women were studied, 18 to 30 years. The MJ users reported no other drug use and alcohol use was negligible in both groups. Urine was positive for metabolites of cannabis only.
The MJ users showed differences in PSG measures (lower total sleep times, and less slow wave sleep than the control group) on both nights; they also showed worse sleep efficiency, longer sleep onset, and shorter REM latency than the control group on Night 2. More sleep continuity parameters were significantly worse for the MJ group than the control group on Night 2 versus Night 1, indicating that sleep in the MJ group was relatively worse on Night 2 compared to Night 1. The MJ group did not show improved sleep after an adaptation night as expected. Withdrawal symptoms, craving, and depression did not appear to influence these findings.
During discontinuation of heavy MJ use, PSG measures of sleep disturbance were detected in MJ users compared with a drug-free control group. While this preliminary study cannot identify the extent to which these group differences were present before abstinence, poor sleep quality either prior to or after MJ discontinuation could result in treatment failure for MJ users. Further investigation is necessary to determine the association between the use and cessation of MJ and sleep disturbance.
No data are available on whether rising carbon dioxide concentration CO₂ or increased air temperature can alter the establishment and persistence of common ragweed (Ambrosia artemisiifolia L.) within ...a plant community following soil disturbance. To determine ragweed longevity, we exposed disturbed soil with a common seed bank population to an in situ temperature and CO₂ gradient along an urban-rural transect beginning in early 2002. No other consistent differences in meteorological variables (e.g. wind speed, humidity, PAR, tropospheric ozone) as a function of urbanization were documented over the course of the study (2002-2005). Above-ground measurements of biomass over this period demonstrated that ragweed along the transect responded to urban induced increases in CO₂/temperature with peak biomass being observed at this location by the end of 2003. However, by the Fall of 2004, and continuing through 2005, urban ragweed populations had dwindled to a few plants. The temporal decline in ragweed populations was not associated with increased disease, herbivory or auto-allelopathy, but was part of a demographic reduction in the total number of annual plant species observed for the urban location. In a separate experiment, we showed that such a demographic shift is consistent with CO₂/temperature induced increases in biomass and litter accumulation, with a subsequent reduction in germination/survival of annual plant species. Overall, these data indicate that CO₂/temperature differences associated with urbanization may increase initial ragweed productivity and pollen production, but suggest that long-term, multi-year persistence of ragweed in the urban macro-environment may be dependent on other factors.
It is necessary to assess whether the management of protected areas is achieving the objectives set for them. In particular, changes and trends in wildlife populations should be documented. We ...compared the 1990 abundance of mammals in two Costa Rican protected areas, Corcovado National Park (CNP) and Golfo Dulce Forest Reserve (GDFR), with similar environmental characteristics but different hunting restrictions and levels of protection. We also monitored the abundance of mammals in CNP over a 4-year period. We also devised an inexpensive method of monitoring tropical rainforest mammal populations in a timely and efficient manner. The method is based on the use of mammal track records and arboreal mammal sightings and requires little effort. With this method 20 mammal species were recorded at CNP and 15 at GDFR. Species were consistently less abundant in GDFR than in CNP, principally those species preferred by hunters. Species were grouped according to whether or not they are used as food and whether they are locally or globally threatened or not threatened. The abundance of all these groups of species in GDFR was 6-28% the abundance in CNP. During 1990-1994, overall mammal abundance in CNP remained relatively stable, but there was considerable variability among species. As a group, both species used for food and globally threatened species declined in abundance during that period in CNP. The abundance of all groups of species declined from 1992 to 1994, coinciding with a reduction in hunting vigilance at CNP. Evidence suggests that the main factor differentiating the abundance of mammals in the two protected areas, and at CNP during the study period, was the level of hunting. Golfo Dulce Forest Reserve seems to be achieving only partial success in protecting wildlife, whereas Corcovado National Park seems to be considerably more effective, although not entirely successful.
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