Friction and wear behaviour of Inconel 718 alloy fabricated by selective laser melting after heat treatments

ABSTRACT

The effect of heat treatments (solution and double aging) on friction and wear behaviour of Inconel 718 (IN718) alloy fabricated by selective laser melting (SLM) were studied. After heat treatment of solution and double aging, the friction and wear of the alloy have been improved. The worn surfaces of heat-treated IN718 alloy became smoother, and micro-ploughing became shallower. After solid solution hearting, a portion of the Laves phase ((Ni, Fe, Co)₂(Nb, Ti, Mo)) dissolves into the matrix, after which the γ″ phase (Ni₃Nb) andthe equilibrium phase of the δ phase (Ni₃Nb) precipitates during double ageing. After solution and double aging, nano-scale γ′ (Ni₃(Al, Ti)) and γ″ phases distribute homogeneously in the matrix, which improves the material hardness and wear resistance of the SLMed IN718 alloy.     

Improving executive function using transcranial infrared laser stimulation

Transcranial infrared laser stimulation is a new non‐invasive form of low‐level light therapy that may have a wide range of neuropsychological applications. It entails using low‐power and high‐energy‐density infrared light from lasers to increase metabolic energy. Preclinical work showed that this intervention can increase cortical metabolic energy, thereby improving frontal cortex‐based memory function in rats. Barrett and Gonzalez‐Lima (2013, Neuroscience, 230, 13) discovered that transcranial laser stimulation can enhance sustained attention and short‐term memory in humans. We extend this line of work to executive function. Specifically, we ask whether transcranial laser stimulation enhances performance in the Wisconsin Card Sorting Task that is considered the gold standard of executive function and is compromised in normal ageing and a number of neuropsychological disorders. We used a laser of a specific wavelength (1,064 nm) that photostimulates cytochrome oxidase – the enzyme catalysing oxygen consumption for metabolic energy production. Increased cytochrome oxidase activity is considered the primary mechanism of action of this intervention. Participants who received laser treatment made fewer errors and showed improved set‐shifting ability relative to placebo controls. These results suggest that transcranial laser stimulation improves executive function and may have exciting potential for treating or preventing deficits resulting from neuropsychological disorders or normal ageing.     

One-step synthesis of bulk quantities of graphene from graphite by femtosecond laser ablation under ambient conditions

Bulk synthesis of few-layer graphene (FLG) for industrial applications still remains a challenge for researchers. Here, we report a very simple technique for bulk synthesis of FLG by femtosecond laser ablation of graphite powder suspended in ethanol without the requirement of a controlled environment. Graphite powder, with an average particle size <20 μm, was suspended uniformly in ethanol and ablated at room temperature using fs pulses (wavelength ~800 nm and an input beam diameter ~8 mm) followed by ultrasonication to obtain FLG with a lateral size of ~1 μm. Raman spectroscopy and high-resolution transmission electron microscopy data confirmed the nature and morphology of the FLG. The quality and number of layers in the FLG could be controlled by tuning the laser parameters.     

理性看待心房颤动导管消融成功率

随着心房颤动导管消融术的发展,其成功率不断提高,但医学上的消融成功并不一定等同于永久性治愈,且由于心房颤动的复杂性、消融终点多元性、不规范的术后随访制度和医疗体制不合理等诸多因素影响,导管消融成功率往往被无意或有意夸大,术后可能会因为达不到患者期望值而产生医疗纠纷。     

阵发性心房颤动导管消融策略

导管消融是目前治疗阵发性心房颤动（房颤）的重要手段。消融策略包括阻断房颤的触发病灶和清除房颤的维持机制。消融方法主要为肺静脉隔离、碎裂电位消融、心房去迷走神经、线性消融及上述方法的联合应用。     

腔内激光疗法联合高位结扎治疗大隐静脉曲张疗效分析

比较大隐静脉腔内激光疗法（EVLT）联合高位结扎术与传统术式的临床疗效。选取大连医科大学附属第二医院2008年2月~2014年2月收治的大隐静脉曲张患者180例,采用EVLT的90例患者为激光组,采用传统高位结扎剥脱治疗的90例患者为对照组。激光组患者手术时间,切口数目及出血量优于对照组（P〈0.05）;两组总体VCSS计分差值、CEAP分布改变无差异,但伴静脉性溃疡病例,激光组VCSS计分差值优于传统组（P〈0.05）;两组术后并发症无差异。EVLT联合高位结扎术综合疗效明显优于传统术式,伴有静脉性溃疡的病例尤其明显。     

Grain growth as a stochastic and curvature-driven process

Grain growth subjected to the interplay of stochastic and curvature-driven mechanisms in a single-phase system has been investigated. Numerical results have shown that when the grains are smaller than several tens of nanometres the dominating mechanism is stochastic diffusion control of boundaries. As the grains grow the influence of the deterministic curvature-driven mechanism increases and finally controls the process. In terms of finite-difference solutions to the Fokker–Planck continuity equation, the predicted grain size approaches a log-normal distribution, which agrees well with experimental observations.     

心房颤动的病因、发病机制与射频导管消融治疗现状

随着人们研究的不断深入,对心房颤动的病因、发病机制有了更新的认识。后者从起搏点兴奋性增高,折返机制,发展到对心肌袖、电重构的认识;以及肺静脉、迷走神经在阵发性心房颤动中的作用,遗传物质异质性及基因突变等。同样,心房颤动的射频导管消融治疗也取得了突破性的进展。     

慢性心房颤动的导管消融治疗

慢性心房颤动（房颤）的发生和维持机制远较阵发性房颤复杂,导管消融治疗方法还在不断完善和优化,消融策略应包括针对房颤触发灶和维持基质的更广泛的消融方法,包括肺静脉前庭消融隔离、复杂碎裂电位消融和线性消融的阶梯式复合消融方法,可提高慢性房颤治疗的有效性。在目前的认识和技术条件下,慢性房颤的导管消融治疗应在有经验的中心完成。     

心房颤动的外科治疗策略

阵发性心房颤动（房颤）需要“局灶触发”,其触发灶一般位于肺静脉开口附近,持续或永久性房颤同时需要“局灶触发”和心房的“异常基质”两个因素。也有人认为持续或永久性房颤根本不需要触发灶。因此,可靠的肺静脉隔离可以治愈绝大部分阵发性房颤的患者,而持续或永久性房颤则需要进行迷宫手术或与其相似的肺静脉隔离基础上的心房附加隔离线。近年来外科消融发展很快,其原因是该方法可达到与迷宫手术相似的高成功率,而并发症低以及手术时间短则明显优于迷宫手术。外科消融可采用的能量很多,有射频、微波、冷冻等。因为外科一般为永久性房颤的患者,肺静脉开口加左房后壁消融是其基本的消融线。考虑到没有心脏器质性疾病的房颤本身是一种良性心律失常,同时外科消融可能出现的某些重并发症,例如左房食管漏、冠状动脉损伤等,不推荐广泛应用外科消融来治疗孤立的房颤。但对需要进行心脏外科手术的患者合并房颤,无论是永久或阵发性房颤,均应常规进行外科治疗。