Ventilation of the Black Sea pycnocline on seasonal and interannual time scales

The paper is a description of temporal variability of winter cooling conditions and estimation of effective cross-isopycnal mixing rates in the Black Sea. Data averaging versus salinity / sigma-t scale was used to filter effects of local dynamics. It is shown that traces of winter mixing events appear well preserved in the temperature-salinity structure, due to the peculiarities of the Black Sea where temperature often acts as a passive tracer with a smaller contribution to density as compared to salinity. Vertical distribution of the magnitudes of temperature oscillations indicates that the convection events have limited effects in modifying the structure of the middle and lower pycnocline on a seasonal time scale. However, long-term fluctuations are well recognised. The magnitudes of the seasonal and long-term temperature fluctuations are comparable only in the upper pycnocline. Three major cooling events can be distinguished from the record of the pycnocline temperature for the past 75 years. The intensive cooling occurred in the late 1920s - early 1930s, early 1950s and late 1980s - early 1990s. Partial renewal of the water of the cold intermediate layer core took place approximately once in two years. The period when convection causes erosion of the pycnocline lasts for only a week. It is shown that a lateral source of heat and salt exists for the upper pycnocline, where it is the cold intermediate water, and for the lower pycnocline, the layer below S@ 20.5, where this lateral source of salt and heat is maintained by disintegrating Bosphorus plume

Investigation of an actively controlled robot arm for vibration suppression in milling

In recent years, the use of robotic systems to enhance the productivity of machining operations has received significant attention from the research and manufacturing communities. Robots have the potential to further improve productivity, for example by providing automated workpiece fixturing, or by providing a flexible and reconfigurable platform from which a variety of subtractive or additive manufacturing operations could be performed. One possible approach is the use of a robotic arm to provide additional fixturing or support of the workpiece during the machining operation. This can increase the stiffness of the workpiece system during machining, which can improve productivity by limiting the onset of undesirable vibrations such as chatter. Chatter is a form of self-excited vibration which leads to low surface quality of the workpiece, shortens the cutting tool life and increases the cutting forces. In this paper, an actively controlled robot arm is simulated in order to suppress the chatter, in an effort to further improve the chatter stability. During the milling operation, preload can be applied through the robot to support the flexible structure, however, the robot cannot suppress high-frequency forces. Since the stiffness and damping ratio of the large flexible structure vary during the operation due to material removal, active vibration control is performed. A proof-mass actuator is proposed that can provide 45 N force up to 2000 Hz with 2 mm stroke. The dynamic properties of the device are identified experimentally as part of a model of a robot fixture prototype. The robotic arm is modelled as a three degree of freedom system; this is combined with a simplified representation of the workpiece dynamics, and the proof-mass actuator, within a Matlab environment. The effect of active control on the chatter stability is evaluated, focussing initially on the use of direct velocity feedback as a control strategy. Estimated chatter stability predictions, along with time, frequency domain simulation results, show that the application of active control method in robotic-assisted machining can suppress the chatter vibrations during machining and hence increase productivity

Flow dynamics and mixing processes in hydraulic jump arrays: Implications for channel-lobe transition zones

A detailed field investigation of a saline gravity current in the southwest Black Sea has enabled the first complete analysis of three-dimensional flow structure and dynamics of a series of linked hydraulic jumps in stratified, density-driven, flows. These field observations were collected using an acoustic Doppler current profiler mounted on an autonomous underwater vehicle, and reveal that internal mixing processes in hydraulic jumps, including flow expansion and recirculation, provide a previously unrecognised mechanism for grain-size sorting and segregation in stratified density-driven flows. Field observations suggest a newly identified type of hydraulic jump, that is a stratified low Froude number (< 1.5–2) subaqueous hydraulic jump, with an enhanced ability to transport sediment downstream of the jump, in comparison to hydraulic jumps in other subaerial and submarine flows. These novel field data underpin a new process-based conceptual model of channel lobe transition zones (CLTZs) that explains the scattered offset nature of scours within such settings, the temporal variations in infill and erosion between adjacent scours, how bed shear stresses are maintained across the CLTZ, and why the locus of deposition is so far downstream of the scour zone

Active chatter suppression through virtual inerter-based passive absorber control

The role of inerter-based devices has generated considerable interest in terms of suppressing the vibrations in machines and structures. The inerter is a mechanical device that generates force proportional to the relative acceleration between its terminals. Recently, it has been shown that inerter-based dynamic vibration absorbers (IDVAs, for the mass ratios between 0 and 0.2) can improve the chatter suppression performance compared to a traditional tuned mass damper (TMD) for the same mass ratios. This study proposes an IDVA applied to machining operations as a novel active control method to increase chatter suppression performance. Considering the TMD application as a virtual passive absorber (VPA) method in active control, IDVAs can be potentially employed in the same framework. A proof-mass actuator, which is mounted on a beam that is designed to support a flexible structure, is proposed. Once the IDVA parameters are optimised, a time-domain model is applied to explore the actuator saturation effects. The effect of an IDVA as a novel active control method on chatter stability is then evaluated. The simulated stability lobe diagram shows that the IDVA increases the absolute chatter stability by just above 20%. To validate the simulation results, an experimental setup is designed including a flexible workpiece to be machined and a proof-mass actuator assembled using a beam. In summary, it is shown that inerter-based dynamic vibration absorbers, as an active control method, can successfully be implemented to improve the chatter suppression performance and critical limiting depth of cut

Spontaneous splenic rupture in an active duty Marine upon return from Iraq: a case report

<p>Abstract</p> <p>Introduction</p> <p>Atraumatic splenic rupture is a rare event that has been associated with several infectious disease processes. In the active duty military population, potential exposure to these pathogens is significant. Here we discuss the case of an active duty Marine with spontaneous splenic rupture upon return from a six-month deployment in Iraq.</p> <p>Case presentation</p> <p>A previously healthy 30-year-old Caucasian male active duty Marine presented with abdominal pain, fever and diarrhea after deployment to Iraq in support of Operation Iraqi Freedom. Based on clinical and radiographic evidence, a diagnosis of spontaneous splenic rupture was ultimately suspected. After exploratory laparotomy with confirmation of rupture, splenectomy was performed, and the patient made a full, uneventful recovery. Histopathologic examination revealed mild splenomegaly with a ruptured capsule of undetermined cause.</p> <p>Conclusion</p> <p>Spontaneous splenic rupture is a rare event that may lead to life-threatening hemorrhage if not diagnosed and treated quickly. Although the cause of this patient's case was unknown, atraumatic splenic rupture has been associated with a variety of infectious diseases and demonstrates some risks the active duty military population may face while on deployment. Having an awareness of these pathogens and their role in splenic rupture, clinicians caring for military personnel must be prepared to recognize and treat this potentially fatal complication.</p

Evaluation of phenolic contents and antioxidant activity of various solvent extracts of Sonchus asper (L.) Hill

<p>Abstract</p> <p>Background</p> <p><it>Sonchus asper </it>(SA) is traditionally used for the treatment of various ailments associated with liver, lungs and kidneys. This study was aimed to investigate the therapeutic potential of nonpolar (hexane, SAHE; ethyl acetate, SAEE and chloroform, SACE) and polar (methanol, SAME) crude extracts of the whole plant.</p> <p>Methods</p> <p>To achieve these goals, several parameters including free-radical (DPPH^•, ABTS^•+, H₂O₂and ^•OH) scavenging, iron chelating activity, scavenging of superoxide radicals, total flavonoids and total phenolic content (TPC) were examined.</p> <p>Results</p> <p>The SA extracts presented a remarkable capacity to scavenge all the tested reactive species with IC₅₀values being found at the μg ⁄ ml level. The SAME was shown to have the highest TPCs while lowest IC₅₀values for the DPPH^•, ABTS^•+radical scavenging capacities and iron chelating scavenging efficiency, moreover, SAME had best activities in scavenging of superoxide radicals and hydrogen peroxide as well as potently scavenged the hydroxyl radicals.</p> <p>Conclusion</p> <p>These results suggest the potential of <it>S. asper </it>as a medicine against free-radical-associated oxidative damage.</p