K+(K0)- Condensation in Highly Dense Matter with the Relativistic Mean-Field Theory

Properties of dense hadronic matter including strange particles are studied within the relativistic mean-field theory (RMFT). The possibility of kaon condensation is reexamined, and a simple condition is found for the parameters included in RMFT.Comment: 12pages, Latex is used, 3 Postscript figures are available by request from [email protected]

Glacier dynamics near the calving front of Bowdoin Glacier, northwestern Greenland

To better understand recent rapid recession of marine-terminating glaciers in Greenland, we performed satellite and field observations near the calving front of Bowdoin Glacier, a 3 km wide outlet glacier in northwestern Greenland. Satellite data revealed a clear transition to a rapidly retreating phase in 2008 from a relatively stable glacier condition that lasted for >20 years. Ice radar measurements showed that the glacier front is grounded, but very close to the floating condition. These results, in combination with the results of ocean depth soundings, suggest bed geometry in front of the glacier is the primary control on the rate and pattern of recent rapid retreat. Presumably, glacier thinning due to atmospheric and/or ocean warming triggered the initial retreat. In situ measurements showed complex short-term ice speed variations, which were correlated with air temperature, precipitation and ocean tides. Ice speed quickly responded to temperature rise and a heavy rain event, indicating rapid drainage of surface water to the bed. Semi-diurnal speed peaks coincided with low tides, suggesting the major role of the hydrostatic pressure acting on the calving face in the force balance. These observations demonstrate that the dynamics of Bowdoin Glacier are sensitive to small perturbations occurring near the calving front

Unsteady Air Bubble Entrainment and Detrainment at a Plunging Breaker: Dominant Time Scales and Similarity of Water Level Variations

At plunging breakers, air bubbles are entrained at the impingement of the water jet, formed at the top of the wave, with the water free surface in front. During the present study, air bubble entrainment at a pseudo-plunging breaker was investigated at near full-scale and further experimental work studied the bubble detrainment process. Experimental observations included the generation and propagation of waves downstream of the plunge point. Experimental results highlighted a number of unsteady air-water flow patterns and emphasise high levels of aeration: i.e., depth-averaged void fraction of more than 10% next to jet impact in shallow waters. Unsteady bubble injection experiments showed a strong vortical motion induced by the rising bubbles. Altogether, the results suggest that a dominant time scale is the bubble rise time d1/ur, which cannot be scaled properly with an undistorted Froude model. The study contributes to a better understanding of unsteady bubble entrainment at a pseudo-plunging breaker and the associated vortical circulation

An Experimental Study of Tsunami Runup on Dry and Wet Horizontal Coastlines

Wave runup generated by a tsunami reaching the shoreline may induce devastating flood waves. When tsunami wave breaking is associated with a plunging jet, some energy dissipation at jet impact and the downstream propagation of the surge is characterised by a high initial momentum resulting from the plunging jet. New experiments were performed in a large-size facility (15-m long 0.8-m wide channel). The experimental data highlight a large wave celerity during the initial stage (i.e. x/do 30), the bore propagates at a speed similar to that predicted by the 'classical' analysis. The results highlight a reduced warning time downstream of plunging breaking wave

A protection method against massive error mails caused by sender spoofed spam mails

Wide spread of spam mails is one of the most serious problems on e-mail environment. Particularly, spam mails with a spoofed sender address should not be left alone, since they make the mail server corresponding to the spoofed address be overloaded with massive error mails generated by the spam mails, and since they waste a lot of network and computer resources. In this paper, we propose a protection method of the mail server against such massive error mails. This method introduces an additional mail server that mainly deals with the error mails in order to reduce the load of the original mail server. This method also provide a function that refuses error mails to these two mail servers to save the network and computer resources

Unsteady Two-Dimensional Orifice Flow: An Experimental Study

Orifice flows were used as water clocks since the Antiquity up to the 16-th century. Today the sand glass uses the same principle with granular material. Orifices and nozzles are used also as measuring discharges. A related form is the sharp-crested weir commonly used for discharge measurement in open channels. Most works were conducted with steady flow conditions and there is little information on the unsteady flow pattern. In this study, the writers describe an experimental investigation of an unsteady orifice flow. The study was conducted in a large-size facility with a rectangular orifice (0.75-m by 0.07-m) discharging up to 1.2 m3 in about 10 seconds. The study is focused on the unsteady flow patterns, the discharge capacity and the velocity field in the reservoir. The results are compared with "classical" orifice flow results

Experimental Investigations of Wave Runup Downstream of Nappe Impact: Applications to Flood Wave Resulting from Dam Overtopping and Tsunami Wave Runup

Flood waves resulting from dam overtopping have been responsible for numerous losses of life (e.g. Vajont dam catastrophe). A related form of flooding is the wave runup generated by a tsunami reaching the shoreline. When dam overtopping or tsunami wave breaking occur, the process is often associated with a free-falling nappe and plunging jet, some energy dissipation at nappe impact and the downstream propagation of the surge. The dominant characteristic of the advancing bore is its high initial momentum resulting from the free-falling nappe or the breaker plunging jet. The wave front usually travels faster than a 'classical' dam break wave because of the higher momentum of the wave.New experiments were performed in a large-size facility (15-m long 0.8-m wide channel). The experimental data highlight the large wave celerity during the initial stage (i.e. x/do 30), the bore propagates at a speed similar to that of a 'classical' dam break wave. New correlations were presented to estimate roughly the wave celerity for x/do < 20 to 25. Altogether the results show a reduced warning time and a greater risk for significant damage and losses of life. The same results are later applied to dam overtopping cases and to tsunami runup applications. It is believed that the proposed correlations provide a more accurate estimate of the horizontal runup close to the nappe impact : i.e., x/do < 30 or x/(H1+h) < 10

Air Bubble Entrainment at Plunging Breakers and Its Effect on Long Period Waves: An Experimental Study

Recently long waves with periods of several minutes have been recognised as an important exciting component to beach erosion, sedimentation in harbours, and oscillations of water and moored ships in harbours. Although long waves are usually involved in a wave train with wave groups as nonlinear bound wave components, the energy of free long waves increases drastically near the surf zone, which implies some energy transfer mechanisms from short to long waves near the shoreline. The present study regards the air bubble entrainment due to plunging breakers as another energy transfer mechanism. Air bubble entrainment by breaking waves is a significant factor in the surf zone under high wave conditions. However the air bubble entrainment process is improperly scaled by a Froude similitude (WOOD 1991, CHANSON 1997), and most laboratory experiments tend to underestimate its effects. During the present study, air bubble entrainment at plunging breakers was investigated in a large-size facility. The breaker plunging jet was modelled by an unsteady vertical jet discharging into a 20-m long wave 0.8-m wide flume. The falling nappe was 0.75-m wide and 0.07-m thick at the orifice and the free-fall height ranged from 0.82 up to 1.32 m. The wave field downstream of the nappe impact was recorded for a range of initial flow conditions : initial water depths, initial water volumes of the pseudo plunging breaker, initial wave field. For some experiments, air entrainment was suppressed by a factor of 2 to 3 by inserting 18-mm thin plastic sheets inhibiting bubble entrainment at the plunging jet impingement. Air entrainment at the plunging jet is associated with a rise in water level caused by the liquid displacement. FUHRBOTER (1990) suggested that the entrained air causes a transfer of energy into potential energy. The subsequent release of that energy may contribute to the generation of 'free' long waves with periods corresponding to the duration of the water level rise. The spatial variation of the water level rise in the wave group might also generate 'free' waves of period equal to the wave group period. In laboratory, the suppression of air entrainment is associated with a reduction of wave energy flux corresponding to about the rise bubble time. Altogether the study demonstrates the generation of 'free' long waves by air entrained at wave breaking