Development of volatile fraction of fresh cut osmotically treated mango during cold storage

The influence of minimal processing by osmotic treatment and cold storage on the volatile profile of mango was studied by comparison with the volatile profile of fresh samples. Osmotic treatments, at atmospheric pressure and by applying a vacuum pulse, were carried out using a 45 Brix sucrose solution with (2%) and without calcium lactate, at 30 °C. Samples were treated until they reached 20 Brix in all cases. The volatile profile of the samples was characterised at 0, 1, 4 and 8 days of cold storage at 10 °C, using purge and trap thermal desorption and GC–MS. Osmotic treatment provokes a decrease in the terpene concentration (the most abundant compounds in the volatile fraction mango) and an increase in ethyl acetate and 1-butanol. This fact was especially observed in treatment applying vacuum impregnation with calcium. Treatment at atmospheric pressure, with calcium in the osmotic solution, was the best way to prevent aroma alterations during processing and to ensure its stability throughout cold storage.     

Effect of plastic permeability and exposure to light during storage on the quality of minimally processed broccoli and cauliflower

The impact of lighting on minimally processed broccoli and cauliflower packaged in four different film types (PVC and three P-Plus) has been measured and compared. The effect on the sensory quality of storage at 4 °C in darkness and under lighting was evaluated. The gas concentration in the packages, pH, mesophilic counts and weight loss was also determined.Neither the type of film used for packaging nor the storage conditions led to changes in the evolution of pH or the microorganism count in broccoli and cauliflower. However, exposure to light stimulated stomatic opening facilitate the exchange of gases between the plant tissue and the atmosphere within the packaging. Thus, a considerable loss of water vapor was observed in the packages of both vegetables stored in the presence of illumination. Moreover, exposure to light stimulated respiratory activity so that for the cauliflower, the composition of the atmosphere within the packages varied depending on the permeability of the packaging film used and the storage conditions. However, in the case of the broccoli, the increase in respiratory activity due to the lighting was compensated by the photosynthetic activity which took place in these conditions, in such a way that the composition of the atmosphere inside the packs solely depended on the permeability of the film.This difference in the physiological response conditioned the most suitable kind of packaging film in each case. For cauliflower, in conditions of darkness, P-Plus 120 film proved the most suitable for preserving its sensory qualities, while under conditions of lighting, this film did not prove suitable due to its low permeability. However, in broccoli the different packaging films tested behaved in a very similar way whether stored under lighting or in the dark.     

微创条件约束下内窥镜操作机器人运动学

研究基于微创条件约束下具有被动式手腕结构机器人运动学,不但可使医生获取同开放式手术中相同的笛卡尔控制方式,而且为机器人系统控制算法研究及轨迹规划奠定了基础.以自行研制的内窥镜操作机器人为例,结合微创手术特殊的应用环境,对机器人运动学进行研究.考虑人体切口处隔肌厚度和病人呼吸等因素对内窥镜插入点位置的影响,给出内窥镜插入点的确定方法.采用几何及矢量代数方法给出机器人位置正逆运动学解析解公式,采用矢量积法求解机器人速度正运动学,基于微创条件约束给出机器人速度逆运动学.为了验证机器人运动学求解的有效性,对内窥镜插入运动及内窥镜绕插入点旋转运动两种典型运动进行试验,应用试验数据对算法进行分析验证,结果显示了运动学算法的有效性.     

Shelf life of fresh-cut Cime di rapa (Brassica rapa L.) as affected by packaging

In this work, the effectiveness of different packaging in prolonging the shelf life of fresh-cut Cime di rapa (Brassica rapa L.) was addressed. Two subsequent experimental trials were run to investigate first the ability of different packaging materials (an oriented polypropylene, a blend of biodegradable polyesters and a nylon/polyethylene multilayer) in delaying the quality loss and then to assess the efficacy of modified atmosphere packaging (MAP). Two different combinations of gas were investigated, oxygen 10%, carbon dioxide 2% and nitrogen 88%, noted as MAP1 and oxygen 8%, carbon dioxide 2% and nitrogen 90%, noted as MAP2. Headspace gas concentration, weight loss, spoilage microbial growth, pH and sensorial quality were monitored in both sets of experiments. The results demonstrated that the best performances under ordinary atmosphere were recorded with the oriented polypropylene-based film, justifying the choice of this polymeric material in the second set-up. The tested MAPs exerted somewhat different results on product quality: the samples packaged under MAP1 recorded a shelf life of 14 days limited by visible moulds, whereas, fresh-cut leaves sealed under MAP2 highlighted a shelf life less than 9 days, due to a high proliferation of total mesophilic bacteria.     

MAX-k-SAT的PTAS归约等价性

通过构造适当的极小不可满足公式,利用子句拼接技术,引入了一个一般化的从k-CNF公式(k≥3)到3-CNF公式之间的归约转换。基于该转换,给出了一个真值指派的转换算法,并证明了MAX-k-SAT与MAX-3-SAT是PTAS归约等价的。因此,对于k,t≥3,MAX-k-SAT与MAX-t-SAT是PTAS归约等价的。     

An active hybrid parallel robot for minimally invasive surgery

During the last years, there has been an increase in research in the field of medical robots. This trend motivated the development of a new robotics field called “robotic-assisted minimally invasive surgery”. The paper presents the kinematic and dynamic behavior of a parallel hybrid surgical robot PARASURG-9M. The robot consists of two subsystems: a surgical robotic arm, PARASURG 5M with five motors, and an active robotized surgical instrument PARASIM with four motors. The methodology for the robot kinematics is presented and the algorithm for robot workspace generation is described. PARASURG-9M inverse dynamic simulation is performed using MSC Adams and finally some numerical and simulation results of the developed experimental model with its system control are also described.     

一种求解布尔不可满足子式的局部搜索算法

解释布尔公式不可满足的原因在众多领域都具有非常重要的理论与应用价值,而不可满足子式能够为公式不可满足的原因提供精确的解释,帮助应用领域的自动化工具迅速定位错误,诊断问题失败的本质缘由。近年来涌现了许多基于SAT求解器DPLL回溯搜索过程的完全算法,但关于不完全方法提取不可满足子式的研究相对较少。因此,本文提出一种采用启发式局部搜索过程从公式的不可满足性证明中求解布尔不可满足子式的算法。该算法根据公式的消解规则通过局部搜索过程直接构造证明不可满足性的消解序列,并融合了布尔推理技术以提高搜索效率;而后通过一个递归过程遍历证明序列从而得到不可满足子式。通过实验与贪心遗传算法进行对比,结果表明本文提出的算法优于贪心遗传算法。     

k-LSAT(k≥3)是NP-完全的(英文)

合取范式(conjunctive normal form,简称CNF)公式F是线性公式,如果F中任意两个不同子句至多有一个公共变元.如果F中的任意两个不同子句恰好含有一个公共变元,则称F是严格线性的.所有的严格线性公式均是可满足的,而对于线性公式类LCNF,对应的判定问题LSAT仍然是NP-完全的.LCNF≥k是子句长度大于或等于k的CNF公式子类,判定问题LSAT≥k的NP-完全性与LCNF≥k中是否含有不可满足公式密切相关.即LSAT≥k的NP-完全性取决于LCNF≥k是否含有不可满足公式.S.Porschen等人用超图和拉丁方的方法构造了LCNF≥3和LCNF≥4中的不可满足公式,并提出公开问题:对于k≥5,LCNF≥k是否含有不可满足公式?将极小不可满足公式应用于公式的归约,引入了一个简单的一般构造方法.证明了对于k≥3,k-LCNF含有不可满足公式,从而证明了一个更强的结果:对于k≥3,k-LSAT是NP-完全的.     

Minimally processed butternut squash shelf life

The effects of dipping in antimicrobial solution and efficacy of proper film and modified atmosphere packaging conditions (MAP) on the quality decay of packaged fresh-cut butternut squash were investigated. The work was divided into three subsequent experimental trials: the first two were aimed to select the optimal packaging film mass transport properties, being micro-perforated and no-perforated films been tested. In the third experimental step, the best film (i.e., no-perforated oriented polypropylene, OPP40) was used to package sliced butternut squash under passive and active MAP. Each slice of product was dipped in aqueous solution of potassium sorbate, while no dipped samples were stored as the controls. During storage at refrigerated temperature (4 ± 1 °C) headspace gas concentrations, mass loss, microbiological and sensory quality were monitored. Results obtained from the preliminary pre-screening showed that micro-perforated films did not match fresh-cut butternut squash respiratory requirements. In these films a high proliferation of moulds occurred, probably due to elevated oxygen levels. Among the no-perforated films with different thickness, the OPP40 showed better performances. In the third trial samples dipped in potassium sorbate and packaged in OPP40 under active MAP recorded a shelf-life of about 22 days respect to the no-dipped samples packaged under both passive and active MAP that reached a shelf life of about 2 weeks.     

Optimum controlled atmospheres minimise respiration rate and quality losses while increase phenolic compounds of baby carrots

Baby carrot is a very perishable product mainly due to the abrasion of the cylindrical carrot root segments. The influence of four different controlled atmospheres (CA) (air, 2 kPa O₂ + 15 kPa CO₂, 5 kPa O₂ + 5 kPa CO₂ and 10 kPa O₂ + 10 kPa CO₂) was studied to maintain quality and prolong the shelf life of baby carrots. Respiration rate (RR), the content of vitamin C, carotenoids and phenolics by HPLC as well as the sensory quality of baby carrots during storage at 4 °C were evaluated. The lowest RR was observed in baby carrots stored under CA containing the lowest O₂ concentrations. Baby carrots under low O₂ atmospheres preserved the highest vitamin C content, as well as the individual carotenoids. The wound-induced phenolic compounds, mainly trans chlorogenic acid, increased two fold in baby carrots stored under 5 kPa O₂ + 5 kPa CO₂. In general, CA maintained the overall visual quality of baby carrots up to 8 days. Controlled atmosphere of 5 kPa O₂ + 5 kPa CO₂ can be recommended as an optimum atmosphere to maintain quality of baby carrots, increasing bioactive compounds such as chlorogenic acid and avoiding anaerobic fermentation in case of temperature abuse.