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81.
This paper describes a security model developed from empirical data collected from a realistic intrusion experiment in which a number of undergraduate students were invited to attack a distributed computer system. Relevant data, with respect to their intrusion activities, were recorded continuously. We have worked out a hypothesis on typical attacker behavior based on experiences from this and other similar experiments. The hypothesis suggests that the attacking process can be split into three phases: the learning phase, the standard attack phase and the innovative attack phase. The probability for successful attacks during the learning phase is expected to be small and, if a breach occurs, it is rather a result of pure luck than deliberate action. During the standard attack phase, this probability is considerably higher, whereas it decreases again in the innovative attack phase. The collected data indicates that the breaches during the standard attack phase are statistically equivalent. Furthermore, the times between breaches seem to be exponentially distributed, which means that traditional methods for reliability modelling of component failures may be applicable 相似文献
82.
Douglas Lynch A.E. Gerard Genello B. Michael Wicks C. 《Aerospace and Electronic Systems Magazine, IEEE》2007,22(1):8-10
This program will develop an automated and unmanned ultra-wide band (UWB) perimeter surveillance sensor designed to provide detection and tracking of personnel and vehicles at the perimeter of critical areas such as military installations and other such facilities. This effort describes the work being done for the protection of high value assets using a compact system which incorporates two technologies to enhance the probability of detection in stressing environments 相似文献
83.
T Takakura E Goto M Tanaka 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(4-5):255-258
An axis clinostat was constructed to create micro and negative gravity also a rotated flat disk was constructed with different rotation rates to give increased gravity, by centrifugal force up to 48 g. Rice seeds were grown on agar in tubes at the constant air temperature of 20 degrees C under an average light condition of 110 micromol/m2/sec(PPF). Humidity was not controlled but was maintained above 90%. Since the tube containers were not large enough for long cultivation, shoot and root growth were observed every 12 hours until the sixth day from seeding. The lengths of shoots and roots for each individual plant were measured on the last day. The stem lengths were increased by microgravity but the root lengths were not. Under the negative gravity, negative orthogeotropism and under microgravity, diageotropism was observed. No significant effect of increased gravity was observed on shoot and root growth. 相似文献
84.
M.A. Sharifi E. Forootan M. Nikkhoo J.L. Awange M. Najafi-Alamdari 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The Caspian Sea has displayed considerable fluctuations in its water level during the past century. Knowledge of such fluctuation is vital for understanding the local hydrological cycles, climate of the region, and construction activities within the sea and along its shorelines. This study established a point-wise satellite altimetry approach to monitor the fluctuations of the Caspian Sea using a complete dataset of TOPEX/Poseidon for the period 1993 to the middle of 2002, and its follow-on Jason-1 for the period 2002 to August 2009. Therefore, 280 virtual time-series were constructed to monitor the fluctuations. The least squares spectral analysis (LSSA) method is, then employed to find the most significant frequencies of the time-series, while the statistical method of principle component analysis (PCA) is applied to extract the dominant variability of level variations. The study also used the observations of TOPEX/Poseidon and Jason-1 over the Volga River along with 5 years of Volga’s water discharge to study its influence on the Caspian Sea level changes. The LSSA results indicate that the lunar semidiurnal (M2) and the Sun semidiurnal (S2) frequencies are the main tidal frequencies of the Caspian Sea with the mean amplitude of 4.2 and 2.8 cm, respectively. A statistically significant long-term frequency (12.5-years period) is also found from altimetry and tide gauge observations. A phase lag, related to the inter-annual frequencies of the Volga River was detected from the point-wise time-series showing level propagation from the northwest to the southeast of the sea. The cross-correlation between the power spectrum of Volga and that of the northern-most, middle, and southern-most points within the Caspian Sea were respectively 0.63, 0.51 and 0.4 of zero-lag correlation, corroborating the influence of the Volga River. The result of PCA also shows that different parts of the Caspian Sea exhibit different amplitudes of level variations, indicating that the point-wise approach, when employing all available satellite measurements could be a suitable method for a preliminary monitoring of this inland water resource as it gives accurate local fluctuations. 相似文献
85.
Orkan Ozcan G.A. Aksu E. Erten N. Musaoglu M. Cetin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(1):160-171
To identify policies that will promote positive effects and mitigate negative ones of grazing is a major challenge in the Silvo-pastoral system. This paper presents the role of examining land-cover change trajectories by remote sensing imagery in grazing policy monitoring. The study was conducted for Duzlercami forest ecosystem located in the Mediterranean geographical region of Turkey and administrated by the General Directorate of Forestry (GDF) of the Ministry of Forestry and Water Affairs. Time series land-cover datasets from Landsat images between 1988 and 2016 were collected and classified. To link the conversions among trajectories and grazing policy, class level landscape metrics derived from the classified images were used. To validate the approach, yearly grazing-plans managed by GDF and populations of livestock were used. Results of this research have indicated that even though there is a yearly grazing plan, overgrazing can happen on the pilot site, and it can be easily identified by the destruction of woody vegetation. The notable correlation (r2?=?0.89) between degraded woody vegetation and cattle population has occurred in the last 30?years in the landscape, and Landsat imagery can effectively support the grazing policy mapping and monitoring. 相似文献
86.
Ch. I. Chaban R. T. Ripetskyj E. L. Kordyum N. A. Kit 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,23(12):2011-2016
Under gravistimulation, dark-grown protonemata of Pottia intermedia revealed negative gravitropism with a growth rate of approximately 28 μm·h−1 at room temperature (20 °C). In 7 days, the protonema formed a bundle of vertically oriented filaments. At an elevated temperature (30 °C), bundles of vertically growing filaments were also formed. However, both filament growth rate and amplitude of the gravicurvature were reduced. Red light (RL) irradiation induced a positive phototropism of most apical protonemal cells at 20 °C. In a following period of darkness, approximately two-thirds of such cells began to grow upward again, recovering their negative gravitropism. RL irradiation at the elevated temperature caused a partial increase in the number of protonemal cells with negative phototropism, but the protonemata did not exhibit negative gravitropism after transfer to darkness. The negative gravitropic reaction was renewed only when protonemata were placed at 20 °C. A dramatic decrease in starch amount in protonemal apical cells, which are sensitive to both gravity and light, occurred at the higher temperature. Such a decrease may be one of the reasons for the inhibition of the protonemal gravireaction at the higher temperature. The observation has a bearing on the starch-statolith theory. 相似文献
87.
A technique for suppressing the ambiguities arising in pulsed scanning systems is described. A system of multiple antennas is employed, and a coded sequence of pulses is radiated. 相似文献
88.
F. G. von der Dunk E. Back-Impallomeni S. Hobe R. M. Ramirez de Arellano 《Space Policy》2004,20(3):149-156
At a time when scientific and commercial interest in the Moon is being reinvigorated it is becoming fashionable for ordinary individuals to ‘buy’ plots on the lunar surface, with the ‘vendors’ arguing that an absence of specific prohibition of individual private activity in space makes such action legal. It is therefore time for the legal community to address this situation by investigating just how legal such activity is—and bringing their findings to the attention of governments. This can be done through an examination of the relationship between national law and international space law, of the provisions of international space law—especially Article 2 of the Outer Space Treaty—and by answering any claims to private ownership of immovable property. Aside from the fact that individuals appear to be being duped, the pursuit of property claims on the Moon could impede future activities aimed at benefiting society. 相似文献
89.
The modulation of galactic cosmic rays in the heliosphere seems to be dominated by four major mechanisms: convection, diffusion, drifts (gradient, curvature and current sheet), and adiabatic energy losses. In this regard the global structure of the solar wind, the heliospheric magnetic field (HMF), the current sheet (HCS), and that of the heliosphere itself play major roles. Individually, the four mechanisms are well understood, but in combination, the complexity increases significantly especially their evolvement with time - as a function of solar activity. The Ulysses observations contributed significantly during the past solar minimum modulation period to establish the relative importance of these major mechanisms, leading to renewed interest in developing more sophisticated numerical models, and in the underlying physics, e.g., what determines the diffusion tensor. With increased solar activity, the relative contributions of the mentioned mechanisms change, but how they change and what causes these changes over an 11-year solar cycle is not well understood. It can therefore be expected that present and forthcoming observations during solar maximum activity will again produce very important insights into the causes of long-term modulation. In this paper the basic theory of solar modulation is reviewed for galactic cosmic rays. The influence of the Ulysses observations on the development of the basic theory and numerical models are discussed, especially those that have challenged the theory and models. Model-based predictions are shown for what might be encountered during the next solar minimum. Lastly, modulation theory and modelling are discussed for periods of maximum solar activity when a global reorganization of the HMF, and the HCS, occurs. This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
90.
K. Kudela V. N. Lutsenko D. G. Sibeck M. Slivka T. V. Gretchko E. T. Sarris 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(12):2849-2854
Time period from October 1996 until January 1998 was checked on high energy resolution DOK2 energetic particle instrument measurements on Interball-1 and Interball-2 for the ion (> 20 keV) dispersive events (EDIS) with the exclusion of Interball-1 orbit parts in the tail. A variety of energy dispersive events, both in ion and electron spectra with different duration is found in the auroral regions, in the outer magnetosphere and near the cusp. While EDIS were observed in all sectors of MLT, the best conditions for their observation were in the afternoon local time. The characteristics of dispersive events observed by DOK2 are consistent with their explanation by the gradient-curvature drift of particles from the injection point(s) in the night local time sector given in Lutsenko at al., 2000a, b. 相似文献