Wireless asymmetric Internet access with a downlink peak bit rate of 10 to 30 Mb/s can be achieved by using the terrestrial digital video broadcasting system (DVB-T) as a supplemental downlink together with today's cellular systems. This paper is a study of dynamic radio resource management on a packet-by-packet basis for this broadband downlink. The dynamic single frequency networks (DSFN) scheme is evaluated. It exploits the macrodiversity capability of the OFDM modulation scheme. The transmitters are dynamically divided into groups of transmitters that send the same information at the same channel frequency simultaneously. The fairly shared spectrum efficiency (FSSE), in bits per second per Hertz per site, which is a combined measurement of maximum throughput and fairness, is evaluated for best-effort traffic. DSFN improves the FSSE by 100% to 370%, for a certain set of test cases, in comparison to the dynamic packet assignment (DPA) scheme, which combines packet scheduling with dynamic channel assignment (DCA).
The ability of a wave energy converter to capture the energy of ocean waves has been studied in offshore experiments. This study covers 50 days during which the converter was subjected to ocean waves over a wide range of frequencies and amplitudes as well as three different electrical loads. The results present the wave energy converter's energy absorption as a function of significant wave height, energy period and electrical load. It is shown that the power generated overall continues to increase with wave amplitude, whereas the relative absorption decreases towards the highest periods and amplitudes. The absorption reached a maximum of approximately 24% with the used combination of buoy, generator and electrical load. Absorption to cover for iron and mechanical losses has not been included. A brief study of the nature of the electromagnetic damping force has also been included in the study. The wave energy converter is of the technology that is being researched at Uppsala University and experimented on off the Swedish west coast at the Lysekil wave energy research site.
Purpose: To explore the possibility of separately quantifying the leakage and scatter components of the peripheral radiation dose resulting from Leksell GammaKnife R Perfexion™ radiotherapy. Methods and Materials: In this study, peripheral dose was defined as the dose arising at points outside the paths of the primary beams. Consider a spherical skull phantom centered at Leksell coordinates (100,100,100). Peripheral dose may arise from: (1) Inphantom scattered radiation originating from primary beams; (2) Radiation first scattered within the collimator structure (3) Photons undergoing multiple scattering and exiting through adjacent collimator openings and (4) Leakage radiation that passes directly through the collimator body. Contributions (1) and (2) were separately quantified via Monte‐Carlo simulations. Types (3) and (4) were measured using EBTII Gafchromic film inserts and placing the sources in“beam‐off” position (i.e. between collimator openings). Additionally, the total peripheral dose arising from a 16‐mm shot was measured using film. The combination of simulated type_1 and type_2 doses and measured type_3 and type_4 were compared to the measured total dose at 40 mm superior and inferior to the isocentre. Results: At the isocentre of the 16‐mm shot, the dose‐rate determined by Monte Carlo simulations agreed with measured dose‐rates to 0.8%, thereby establishing consistency between measurement and simulation. The simulated sum of Type_1 and Type_2 contributions at 40 mm inferior and superior to the isocentre was 0.40% and 0.35% of the isocentre dose‐rate, respectively. Of those totals, 87% was Type_1 a 13% came from Type 2. The measured total peripheral dose‐rate was 0.40% and 0.38% at 40 mm inferiorly and superiorly, respectively. The measured Type_3 and Type_4 dose‐rates were less than 0.01% of the isocentre dose‐rate in either direction. Conclusion: The results of this study indicate that peripheral dose arising from a single 16‐mm shot arises primarily from Type_1, with <0.01% contribution from leakage radiation.
The OFDM based terrestrial digital video broadcasting system (DVB-T) can be utilized for asymmetric Internet access with a downlink peak bit rate of 10-20Mbps. A narrow-band cellular communications system cam be used as uplink. This paper is a comparison of centralized dynamic radio resource management schemes for this downlink packet radio system. Spectrum efficiency in bit/s/Hz/transmitter, and fairly shared spectrum efficiency in bit/s/Hz/transmitter, are evaluated for a best-effort traffic snapshot model. The dynamic packet assignment (DPA) algorithm performs combined packet scheduling and rapid dynamic channel allocation. Even better performance is achieved by the dynamic single frequency networks (DSFN) scheme. It exploits the macro-diversity capability of OFDM modulation. The base station transmitters are dynamically divided into groups that send the same information at the same channel frequency simultaneously.
To study the extent of deep venous thrombosis (DVT) and thrombus regression over time and to compare the results obtained with different diagnostic techniques.A prospective follow-up study with repeated examinations during a 6-month period.Patients studied at clinical vascular laboratories.Forty patients hospitalised for acute DVT. Thirty-six of these completed the follow-up period.The diagnosis of DVT was confirmed with phlebographic and/or ultrasonographic techniques. The patient were then re-examined with colour duplex ultrasound and venous occlusion plethysmography after one week, 3 months and 6 months and with phlebography after 1 week and 6 months. The extent of DVT and number of occluded segments were determined with phlebographic and ultrasonographic techniques. Venous occlusion plethysmography was used to evaluate the functional degree of outflow obstruction.Colour duplex scanning at 3 months' and 6 months' follow-up showed that 55% and 74% of initially occlusive thrombi, respectively, were recanalized, with thrombus resolution occurring faster and more completely in those initially limited to popliteal and/or calf level. Discrepancies between phlebography and duplex scanning were found in 6% (26/441) of venous segments investigated by both methods, primarily concerning flow in the veins below the knee.In comparison with phlebography, colour duplex scanning is an accurate method for evaluation and follow-up of patients with DVT. The non-invasive nature of colour duplex scanning makes this method extremely suitable for repeated studies and thus a potentially very valuable tool for both clinical and research studies of circulatory changes involved in acute and chronic DVT.
