In laser and electron-beam welding, a deep cavity called a keyhole or beam hole is formed in the weld pool due to the intense recoil pressure of evaporation. The formation of the keyhole leads to a deep penetration weld with a high aspect ratio and this is the most advantageous feature of welding by high-energy-density beams. However, a hole drilled in a liquid is primarily unstable by its nature and the instability of the keyhole also causes the formation of porosity or cavities in the weld metal. In particular, the porosity formation is one of the serious problems in very high-power laser welding, but its mechanism has not been well understood. The authors have conducted systematic studies on observation of keyhole as well as weld pool dynamics and their related phenomena to reveal the mechanism of porosity formation and its suppression methods. The article will describe the real-time observation of keyhole and plume behaviors in the pulsed and continuous-wave laser welding by high-speed optical and x-ray transmission methods, the cavity formation process and its suppression measures.

ObjectiveDementia is a major public health problem. More and more patients with dementia are being admitted to acute care hospitals for treatment of comorbidities. Issues associated with care of patients with dementia in acute care hospitals have not been adequately clarified. This study aimed to explore the challenges nurses face in providing care to patients with dementia in acute care hospitals in Japan.MethodsThis was a qualitative study using focus group interviews (FGIs). The setting was six acute hospitals with surgical and medical wards in the western region of Japan. Participants were nurses in surgical and internal medicine wards, excluding intensive care units. Nurses with less than 3 years working experience, those without experience in dementia patient care in their currently assigned ward, and head nurses were excluded from participation. FGIs were used to collect data from February to December 2008. Interviews were scheduled for 1–1.5 h. The qualitative synthesis method was used for data analysis.ResultsIn total, 50 nurses with an average experience of 9.8 years participated. Eight focus groups were formed. Issues in administering care to patients with dementia at acute care hospitals were divided into seven groups. Three of these groups, that is, problematic patient behaviors, recurrent problem, and problems affecting many people equally, interact to result in a burdensome cycle. This cycle is exacerbated by lack of nursing experience and lack of organization in hospitals. In coping with this cycle, the nurses develop protection plans for themselves and for the hospital.ConclusionsThe two main issues experienced by nurses while administering care to patients with dementia in acute care hospitals were as follows: (a) the various problems and difficulties faced by nurses were interactive and caused a burdensome cycle, and (b) nurses do their best to adapt to these conditions despite feeling conflicted.

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Laser welding can produce a deeply penetrated bead at high speed. However, in high power cw CO2 laser welding, the characteristic porosity is easily formed in the weld metal, but its formation mechanism has not been well understood. Therefore, the authors have conducted systematic studies of the elucidation of porosity formation mechanism and the development of preventive remedies. They have revealed that many bubbles are formed, mainly from the bottom tip of the keyhole by intense evaporation of the metal. It has also been revealed that the keyhole fluctuates frequently and changes its size and shape, corresponding to the intermittent bubble formation. The majority of bubbles are trapped at the solidifying front in the rear part of the molten pool. However, there are few reports that deal with the simultaneous observation of keyhole and plasma dynamic behavior as well as the formation of bubbles and porosity. In this study, therefore, the interrelationship between keyhole and plasma behavior was examined by using two synchronized high-speed cameras and an x-ray transmission observation system. Especially, the effect of shielding gas on porosity formation was investigated in terms of plasma and keyhole behavior. In the case of He shielding gas, metallic plasma emanated from a keyhole, and the keyhole was open continuously. On the other hand, in the case of N2 shielding gas, a big gas plasma was formed above the weld bead periodically, and metallic plasma and keyhole disappeared just like in the pulsed laser welding. Such periodical interval and duty were different depending on the materials used and exerted an effect on porosity formation tendency.

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