Thirty per cent of all colorectal tumours develop in the rectum.The location of the rectum within the bony pelvis and its proximity to vital structures presents significant therapeutic challenges when considering neoa...Thirty per cent of all colorectal tumours develop in the rectum.The location of the rectum within the bony pelvis and its proximity to vital structures presents significant therapeutic challenges when considering neoadjuvant options and surgical interventions.Most patients with early rectal cancer can be adequately managed by surgery alone.However,a significant proportion of patients with rectal cancer present with locally advanced disease and will potentially benefit from down staging prior to surgery.Neoadjuvant therapy involves a variety of options including radiotherapy,chemotherapy used alone or in combination.Neoadjuvant radiotherapy in rectal cancer has been shown to be effective in reducing tumour burden in advance of curative surgery.The gold standard surgical rectal cancer management aims to achieve surgical removal of the tumour and all draining lymph nodes,within an intact mesorectal package,in order to minimise local recurrence.It is critically important that all rectal cancer cases are discussed at a multidisciplinary meeting represented by all relevant specialties.Pre-operative staging including CT thorax,abdomen,pelvis to assess for distal disease and magnetic resonance imaging to assess local involvement is essential.Staging radiology and MDT discussion are integral in identifying patients who require neoadjuvant radiotherapy.While Neoadjuvant radiotherapy is potentially beneficial it may also result in morbidity and thus should be reserved for those patients who are at a high risk of local failure,which includes patients with nodal involvement,extramural venous invasion and threatened circumferential margin.The aim of this review is to discuss the role of neoadjuvant radiotherapy in the management of rectal cancer.展开更多
According to the main international clinical guidelines,the recommended treatment for locally-advanced rectal cancer is neoadjuvant chemoradiotherapy followed by surgery.However,doubts have been raised about the appro...According to the main international clinical guidelines,the recommended treatment for locally-advanced rectal cancer is neoadjuvant chemoradiotherapy followed by surgery.However,doubts have been raised about the appropriate definition of clinical complete response(cCR)after neoadjuvant therapy and the role of surgery in patients who achieve a cCR.Surgical resection is associated with significant morbidity and decreased quality of life(QoL),which is especially relevant given the favourable prognosis in this patient subset. Accordingly, therehas been a growing interest in alternative approaches with less morbidity,including the organ-preserving watch and wait strategy, in which surgery isomitted in patients who have achieved a cCR. These patients are managed with aspecific follow-up protocol to ensure adequate cancer control, including the earlyidentification of recurrent disease. However, there are several open questionsabout this strategy, including patient selection, the clinical and radiologicalcriteria to accurately determine cCR, the duration of neoadjuvant treatment, therole of dose intensification (chemotherapy and/or radiotherapy), optimal followupprotocols, and the future perspectives of this approach. In the present review,we summarize the available evidence on the watch and wait strategy in thisclinical scenario, including ongoing clinical trials, QoL in these patients, and thecontroversies surrounding this treatment approach.展开更多
Background：Pediatric emergency rooms （PERs） in Chinese hospitals are perpetually full of sick and injured children because of the lack of sufficiently developed community hospitals and low access to family physicia...Background：Pediatric emergency rooms （PERs） in Chinese hospitals are perpetually full of sick and injured children because of the lack of sufficiently developed community hospitals and low access to family physicians.The aim of this study was to evaluate the clinical value of a new five-level Chinese pediatric emergency triage system （CPETS）,modeled after the Canadian Triage System and Acuity Scale.Methods：In this study,we compared CPETS outcomes in our PER relative to those of the prior two-level system.Patients who visited our PER before （January 2013-June 2013） and after （January 2014-June 2014） the CPETS was implemented served as the control and experimental group,respectively.Patient flow,triage rates,triage accuracy,wait times （overall and for severe patients）,and patient/family satisfaction were compared between the two groups.Results：Relative to the performance of the former system experienced by the control group,the CPETS experienced by the experimental group was associated with a reduced patient flow through the PER （Cox-Stuart test,t =0,P 〈 0.05）,a higher triage rate （93.40% vs.90.75%;χ^2 =801.546,P 〈 0.001）,better triage accuracy （96.32% vs.85.09%;χ^2 =710.904,P 〈 0.001）,shorter overall wait times （37.30 ± 13.80 min vs.41.60 ± 15.40 min;t =11.27,P 〈 0.001）,markedly shorter wait times for severe patients （2.07 [0.65,4.11] min vs.3.23 [1.90,4.36] min;z =-2.057,P =0.040）,and higher family satisfaction rates （94.23% vs.92.21%;x2 =321.528,P 〈 0.001）.Conclusions：Implementing the CPETS improved nurses＇ abilities to triage severe patients and,thus,to deliver the urgent treatments more quickly.The system shunted nonurgent patients to outpatient care effectively,resulting in improved efficiency of PER health-care delivery.展开更多
This paper studies the hybrid flow-shop scheduling problem with no-wait restrictions. The production process consists of two machine centers, one has a single machine and the other has more than one parallel machine....This paper studies the hybrid flow-shop scheduling problem with no-wait restrictions. The production process consists of two machine centers, one has a single machine and the other has more than one parallel machine. A greedy heuristic named least deviation algorithm is designed and its worst case performance is analyzed. Computational results are also given to show the algorithm's average performance compared with some other algorithms. The least deviation algorithm outperforms the others in most cases tested here, and it is of low computational complexity and is easy to carry out,thus it is of favorable application value.展开更多
In 2014, there were an estimated 136800 new cases of colorectal cancer, making it the most common gastrointestinal malignancy. It is the second leadingcause of cancer death in both men and women in the United States a...In 2014, there were an estimated 136800 new cases of colorectal cancer, making it the most common gastrointestinal malignancy. It is the second leadingcause of cancer death in both men and women in the United States and over one-third of newly diagnosed patients have stage Ⅲ(node-positive) disease. For stage Ⅱ and Ⅲ colorectal cancer patients, the mainstay of curative therapy is neoadjuvant therapy, followed by radical surgical resection of the rectum. However, the consequences of a proctectomy, either by low anterior resection or abdominoperineal resection, can lead to very extensive comorbidities, such as the need for a permanent colostomy, fecal incontinence, sexual and urinary dysfunction, and even mortality. Recently, trends of complete regression of the rectal cancer after neoadjuvant chemoradiation therapy have been confirmed by clinical and radiographic evaluationthis is known as complete clinical response(cC R). The "watch and wait" approach was first proposed by Dr. Angelita Habr-Gama in Brazil in 2009. Those patients with c CR are followed with close surveillance physical examinations, endoscopy, and imaging. Here, we review management of rectal cancer, the development of the "watch and wait" approach and its outcomes.展开更多
Locally advanced rectal cancer requires a multidisciplinary approach based on total neoadjuvant treatment with radiotherapy(RT)and chemotherapy(ChT),followed by deferred surgery.Currently,alternatives to the standard ...Locally advanced rectal cancer requires a multidisciplinary approach based on total neoadjuvant treatment with radiotherapy(RT)and chemotherapy(ChT),followed by deferred surgery.Currently,alternatives to the standard total neoadjuvant therapy(TNT)are being explored,such as new ChT regimens or the introduction of immunotherapy.With standard TNT,up to a third of patients may achieve a complete pathological response(CPR),potentially avoiding surgery.However,as of now,we lack predictive markers of response that would allow us to define criteria for a conservative organ strategy.The presence of muta-tions,genes,or new imaging tests is helping to define these criteria.An example of this is the diffusion coefficient in the diffusion-weighted sequence of magnetic resonance imaging and the integration of this imaging technique into RT treatment.This allows for the monitoring of the evolution of this coefficient over successive RT sessions,helping to determine which patients will achieve CPR or those who may require intensification of neoadjuvant therapy.展开更多
Neuroendocrine neoplasms(NENs) are a group of rare and heterogeneous malignancies, which can develop in various organs. The clinical course of NENs is quite heterogeneous, with different spontaneous growth rates after...Neuroendocrine neoplasms(NENs) are a group of rare and heterogeneous malignancies, which can develop in various organs. The clinical course of NENs is quite heterogeneous, with different spontaneous growth rates after diagnosis, and different degrees of sensitivity to the same therapy even when they have similar characteristics. Watch and wait(W and W), is a term coined to indicate observation being conducted to assess the evolution of the tumor without administering any anti-tumor therapy. It has been applied to NENs since in extremely rare cases they tend to remain stable for a long time. Although W and W has been reported in several guidelines and recommendations it has never been validated, nor has it been specifically investigated. Furthermore it is not standardized. Therefore its application in clinical practice can differ in terms of tumor status assessment, type and timing of imaging or other exams utilized. In conclusion, while undertaking W and W to delay the first-line therapy by some weeks may be justified in good performance asymptomatic patients with low-grade NENs in order to usefully characterize the disease and patient and thereby choose the best therapy and therapeutic strategy, it seems to be far more difficult to justify W and W with the intent of avoiding an anti-tumor treatment. It should be considered that not only do NENs tend to grow even when they have very favorable biological characteristics but also that the alternative to W and W is most commonly a low toxic and effective treatment with somatostatin analogs.展开更多
BACKGROUND Familial dilated cardiomyopathy(FDCM) account for 20%-30% of non-ischemic cardiomyopathies(NICM). Previous published data showed that some patients with FDCM tend to have rapidly progressive disease; howeve...BACKGROUND Familial dilated cardiomyopathy(FDCM) account for 20%-30% of non-ischemic cardiomyopathies(NICM). Previous published data showed that some patients with FDCM tend to have rapidly progressive disease; however, five-year mortality was not significantly different in the familial and non-familial forms of NICM with optimal medical therapy.AIM To better define the characteristics and clinical outcomes of FDCM patients listed for heart transplantation(HT).METHODS We queried the United Network for Organ Sharing Registry to identify FDCM patients listed for HT between January 2008 and September 2015 and compared them to NICM and ischemic cardiomyopathy(ICM) patients. We included all patients ≥ 18 years old and we separated patients to three groups: FDCM, NICM and ICM. Chi-square test was used to compare between categorical variables, the t-test was used to compare between continues variables, and Cox-proportional hazards model was used to perform time-dependent survival analyses.RESULTS Of the 24809 adults listed for HT, we identified 677 patients(2.7%) with the diagnosis of FDCM. Compared to patients with NICM and ICM, FDCM patients were younger(FDCM 43.9 ± 13.5 vs NICM 50.9 ± 12.3, P < 0.001, vs ICM 58.5 ±8.1, P < 0.001), more frequently listed as status 2(FDCM 35.2% vs NICM 26.5%, P< 0.001), with significantly lower left ventricular assist device(LVAD) utilization(FDCM 18.4% vs NICM 25.1%, P < 0.001; vs ICM 25.6%, P < 0.001), but higher use of total artificial heart(FDCM 1.3% vs NICM 0.6%, P = 0.039; vs ICM 0.4%, P =0.002). Additionally, patients with FDCM were less frequently delisted for clinical deterioration or death and more likely to be transplanted compared to those with NICM [hazard ratio(HR): 0.617, 95% confidence interval(CI): 0.47-0.81; HR: 1.25,95%CI: 1.14-1.37, respectively], and ICM(HR: 0.5, 95%CI: 0.38-0.66; HR: 1.18,95%CI: 1.08-1.3, respectively). There was more frequent rejection among patients with FDCM(FDCM 11.4% vs NICM 9.8%, P = 0.28; vs ICM 8.4%, P = 0.034). One,three, and five po展开更多
In this paper, we consider the replacement of a single unit with catastrophic failure mode. Besides replaced at a preset time, the unit is also replaced at failure time or if it encounters a production wait and its ag...In this paper, we consider the replacement of a single unit with catastrophic failure mode. Besides replaced at a preset time, the unit is also replaced at failure time or if it encounters a production wait and its age has reached a threshold. The joint preventive maintenance interval and threshold optimization problem are formulated with the objective of minimizing the expected cost per unit time in long run. A numerical example is presented to illustrate the applicability of the model.展开更多
A technique is developed for finding a closed form expression for the cumulative distribution function of the maximum value of the objective function in a stochastic linear programming problem, where either the object...A technique is developed for finding a closed form expression for the cumulative distribution function of the maximum value of the objective function in a stochastic linear programming problem, where either the objective function coefficients or the right hand side coefficients are continuous random vectors with known probability distributions. This is the “wait and see” problem of stochastic linear programming. Explicit results for the distribution problem are extremely difficult to obtain;indeed, previous results are known only if the right hand side coefficients have an exponential distribution [1]. To date, no explicit results have been obtained for stochastic c, and no new results of any form have appeared since the 1970’s. In this paper, we obtain the first results for stochastic c, and new explicit results if b an c are stochastic vectors with an exponential, gamma, uniform, or triangle distribution. A transformation is utilized that greatly reduces computational time.展开更多
为了充分利用DTN中各节点资源,减少Epidemic Routing、spray and wait中不区分各节点资源不同,提出了一个基于节点密度、节点运动速度、生存期、节点缓存大小诸多因素,来进行消息转发的算法multi。通过仿真实验表明,multi算法较Epidemic...为了充分利用DTN中各节点资源,减少Epidemic Routing、spray and wait中不区分各节点资源不同,提出了一个基于节点密度、节点运动速度、生存期、节点缓存大小诸多因素,来进行消息转发的算法multi。通过仿真实验表明,multi算法较Epidemic Routing、spray and wait算法在消息成功传输率、平均延迟、网络开销、消息在缓存中滞留的时间上都有明显改善。展开更多
机会网络利用节点移动形成的通信机会来逐步传输消息.然而当机会网络应用在海洋上时,由于海域广阔,节点分布稀疏,所以船舶之间相遇通信的概率较低,同时由于船速较慢,固定航道,传统机会网络路由协议执行效率不高.利用船舶位置信息和航行...机会网络利用节点移动形成的通信机会来逐步传输消息.然而当机会网络应用在海洋上时,由于海域广阔,节点分布稀疏,所以船舶之间相遇通信的概率较低,同时由于船速较慢,固定航道,传统机会网络路由协议执行效率不高.利用船舶位置信息和航行方向等,结合插值算法预测节点未来可能到达的位置,并对Spray and Wait协议改进,从而增加数据传递到目的船舶的可能性和效率,提高了船舶机会网络连通性.最后,通过仿真实验与目前比较流行的机会网络路由协议进行比较,取得较好的实验结果.展开更多
基金Supported by NBCRI,Symptomatic Breast Unit,University Hospital Galway
文摘Thirty per cent of all colorectal tumours develop in the rectum.The location of the rectum within the bony pelvis and its proximity to vital structures presents significant therapeutic challenges when considering neoadjuvant options and surgical interventions.Most patients with early rectal cancer can be adequately managed by surgery alone.However,a significant proportion of patients with rectal cancer present with locally advanced disease and will potentially benefit from down staging prior to surgery.Neoadjuvant therapy involves a variety of options including radiotherapy,chemotherapy used alone or in combination.Neoadjuvant radiotherapy in rectal cancer has been shown to be effective in reducing tumour burden in advance of curative surgery.The gold standard surgical rectal cancer management aims to achieve surgical removal of the tumour and all draining lymph nodes,within an intact mesorectal package,in order to minimise local recurrence.It is critically important that all rectal cancer cases are discussed at a multidisciplinary meeting represented by all relevant specialties.Pre-operative staging including CT thorax,abdomen,pelvis to assess for distal disease and magnetic resonance imaging to assess local involvement is essential.Staging radiology and MDT discussion are integral in identifying patients who require neoadjuvant radiotherapy.While Neoadjuvant radiotherapy is potentially beneficial it may also result in morbidity and thus should be reserved for those patients who are at a high risk of local failure,which includes patients with nodal involvement,extramural venous invasion and threatened circumferential margin.The aim of this review is to discuss the role of neoadjuvant radiotherapy in the management of rectal cancer.
文摘According to the main international clinical guidelines,the recommended treatment for locally-advanced rectal cancer is neoadjuvant chemoradiotherapy followed by surgery.However,doubts have been raised about the appropriate definition of clinical complete response(cCR)after neoadjuvant therapy and the role of surgery in patients who achieve a cCR.Surgical resection is associated with significant morbidity and decreased quality of life(QoL),which is especially relevant given the favourable prognosis in this patient subset. Accordingly, therehas been a growing interest in alternative approaches with less morbidity,including the organ-preserving watch and wait strategy, in which surgery isomitted in patients who have achieved a cCR. These patients are managed with aspecific follow-up protocol to ensure adequate cancer control, including the earlyidentification of recurrent disease. However, there are several open questionsabout this strategy, including patient selection, the clinical and radiologicalcriteria to accurately determine cCR, the duration of neoadjuvant treatment, therole of dose intensification (chemotherapy and/or radiotherapy), optimal followupprotocols, and the future perspectives of this approach. In the present review,we summarize the available evidence on the watch and wait strategy in thisclinical scenario, including ongoing clinical trials, QoL in these patients, and thecontroversies surrounding this treatment approach.
文摘Background：Pediatric emergency rooms （PERs） in Chinese hospitals are perpetually full of sick and injured children because of the lack of sufficiently developed community hospitals and low access to family physicians.The aim of this study was to evaluate the clinical value of a new five-level Chinese pediatric emergency triage system （CPETS）,modeled after the Canadian Triage System and Acuity Scale.Methods：In this study,we compared CPETS outcomes in our PER relative to those of the prior two-level system.Patients who visited our PER before （January 2013-June 2013） and after （January 2014-June 2014） the CPETS was implemented served as the control and experimental group,respectively.Patient flow,triage rates,triage accuracy,wait times （overall and for severe patients）,and patient/family satisfaction were compared between the two groups.Results：Relative to the performance of the former system experienced by the control group,the CPETS experienced by the experimental group was associated with a reduced patient flow through the PER （Cox-Stuart test,t =0,P 〈 0.05）,a higher triage rate （93.40% vs.90.75%;χ^2 =801.546,P 〈 0.001）,better triage accuracy （96.32% vs.85.09%;χ^2 =710.904,P 〈 0.001）,shorter overall wait times （37.30 ± 13.80 min vs.41.60 ± 15.40 min;t =11.27,P 〈 0.001）,markedly shorter wait times for severe patients （2.07 [0.65,4.11] min vs.3.23 [1.90,4.36] min;z =-2.057,P =0.040）,and higher family satisfaction rates （94.23% vs.92.21%;x2 =321.528,P 〈 0.001）.Conclusions：Implementing the CPETS improved nurses＇ abilities to triage severe patients and,thus,to deliver the urgent treatments more quickly.The system shunted nonurgent patients to outpatient care effectively,resulting in improved efficiency of PER health-care delivery.
基金Supported by the National Natural Science Foundationof China( No. 6 990 40 0 7)
文摘This paper studies the hybrid flow-shop scheduling problem with no-wait restrictions. The production process consists of two machine centers, one has a single machine and the other has more than one parallel machine. A greedy heuristic named least deviation algorithm is designed and its worst case performance is analyzed. Computational results are also given to show the algorithm's average performance compared with some other algorithms. The least deviation algorithm outperforms the others in most cases tested here, and it is of low computational complexity and is easy to carry out,thus it is of favorable application value.
文摘In 2014, there were an estimated 136800 new cases of colorectal cancer, making it the most common gastrointestinal malignancy. It is the second leadingcause of cancer death in both men and women in the United States and over one-third of newly diagnosed patients have stage Ⅲ(node-positive) disease. For stage Ⅱ and Ⅲ colorectal cancer patients, the mainstay of curative therapy is neoadjuvant therapy, followed by radical surgical resection of the rectum. However, the consequences of a proctectomy, either by low anterior resection or abdominoperineal resection, can lead to very extensive comorbidities, such as the need for a permanent colostomy, fecal incontinence, sexual and urinary dysfunction, and even mortality. Recently, trends of complete regression of the rectal cancer after neoadjuvant chemoradiation therapy have been confirmed by clinical and radiographic evaluationthis is known as complete clinical response(cC R). The "watch and wait" approach was first proposed by Dr. Angelita Habr-Gama in Brazil in 2009. Those patients with c CR are followed with close surveillance physical examinations, endoscopy, and imaging. Here, we review management of rectal cancer, the development of the "watch and wait" approach and its outcomes.
文摘Locally advanced rectal cancer requires a multidisciplinary approach based on total neoadjuvant treatment with radiotherapy(RT)and chemotherapy(ChT),followed by deferred surgery.Currently,alternatives to the standard total neoadjuvant therapy(TNT)are being explored,such as new ChT regimens or the introduction of immunotherapy.With standard TNT,up to a third of patients may achieve a complete pathological response(CPR),potentially avoiding surgery.However,as of now,we lack predictive markers of response that would allow us to define criteria for a conservative organ strategy.The presence of muta-tions,genes,or new imaging tests is helping to define these criteria.An example of this is the diffusion coefficient in the diffusion-weighted sequence of magnetic resonance imaging and the integration of this imaging technique into RT treatment.This allows for the monitoring of the evolution of this coefficient over successive RT sessions,helping to determine which patients will achieve CPR or those who may require intensification of neoadjuvant therapy.
文摘Neuroendocrine neoplasms(NENs) are a group of rare and heterogeneous malignancies, which can develop in various organs. The clinical course of NENs is quite heterogeneous, with different spontaneous growth rates after diagnosis, and different degrees of sensitivity to the same therapy even when they have similar characteristics. Watch and wait(W and W), is a term coined to indicate observation being conducted to assess the evolution of the tumor without administering any anti-tumor therapy. It has been applied to NENs since in extremely rare cases they tend to remain stable for a long time. Although W and W has been reported in several guidelines and recommendations it has never been validated, nor has it been specifically investigated. Furthermore it is not standardized. Therefore its application in clinical practice can differ in terms of tumor status assessment, type and timing of imaging or other exams utilized. In conclusion, while undertaking W and W to delay the first-line therapy by some weeks may be justified in good performance asymptomatic patients with low-grade NENs in order to usefully characterize the disease and patient and thereby choose the best therapy and therapeutic strategy, it seems to be far more difficult to justify W and W with the intent of avoiding an anti-tumor treatment. It should be considered that not only do NENs tend to grow even when they have very favorable biological characteristics but also that the alternative to W and W is most commonly a low toxic and effective treatment with somatostatin analogs.
文摘BACKGROUND Familial dilated cardiomyopathy(FDCM) account for 20%-30% of non-ischemic cardiomyopathies(NICM). Previous published data showed that some patients with FDCM tend to have rapidly progressive disease; however, five-year mortality was not significantly different in the familial and non-familial forms of NICM with optimal medical therapy.AIM To better define the characteristics and clinical outcomes of FDCM patients listed for heart transplantation(HT).METHODS We queried the United Network for Organ Sharing Registry to identify FDCM patients listed for HT between January 2008 and September 2015 and compared them to NICM and ischemic cardiomyopathy(ICM) patients. We included all patients ≥ 18 years old and we separated patients to three groups: FDCM, NICM and ICM. Chi-square test was used to compare between categorical variables, the t-test was used to compare between continues variables, and Cox-proportional hazards model was used to perform time-dependent survival analyses.RESULTS Of the 24809 adults listed for HT, we identified 677 patients(2.7%) with the diagnosis of FDCM. Compared to patients with NICM and ICM, FDCM patients were younger(FDCM 43.9 ± 13.5 vs NICM 50.9 ± 12.3, P < 0.001, vs ICM 58.5 ±8.1, P < 0.001), more frequently listed as status 2(FDCM 35.2% vs NICM 26.5%, P< 0.001), with significantly lower left ventricular assist device(LVAD) utilization(FDCM 18.4% vs NICM 25.1%, P < 0.001; vs ICM 25.6%, P < 0.001), but higher use of total artificial heart(FDCM 1.3% vs NICM 0.6%, P = 0.039; vs ICM 0.4%, P =0.002). Additionally, patients with FDCM were less frequently delisted for clinical deterioration or death and more likely to be transplanted compared to those with NICM [hazard ratio(HR): 0.617, 95% confidence interval(CI): 0.47-0.81; HR: 1.25,95%CI: 1.14-1.37, respectively], and ICM(HR: 0.5, 95%CI: 0.38-0.66; HR: 1.18,95%CI: 1.08-1.3, respectively). There was more frequent rejection among patients with FDCM(FDCM 11.4% vs NICM 9.8%, P = 0.28; vs ICM 8.4%, P = 0.034). One,three, and five po
基金the National Natural Science Foundation of China(Nos.11426084,11001005,71231001,71301009 and 71420107023)the China Postdoctoral Science Foundation Funded Project(No.2013M530531)+2 种基金the Natural Science Foundation of Hebei Province(No.A2014208133)the Foundation of Hebei Education Department(No.QN2014132)the Ministry of Education Doctor of Philosophy Supervisor Fund(No.20120006110025)
文摘In this paper, we consider the replacement of a single unit with catastrophic failure mode. Besides replaced at a preset time, the unit is also replaced at failure time or if it encounters a production wait and its age has reached a threshold. The joint preventive maintenance interval and threshold optimization problem are formulated with the objective of minimizing the expected cost per unit time in long run. A numerical example is presented to illustrate the applicability of the model.
文摘A technique is developed for finding a closed form expression for the cumulative distribution function of the maximum value of the objective function in a stochastic linear programming problem, where either the objective function coefficients or the right hand side coefficients are continuous random vectors with known probability distributions. This is the “wait and see” problem of stochastic linear programming. Explicit results for the distribution problem are extremely difficult to obtain;indeed, previous results are known only if the right hand side coefficients have an exponential distribution [1]. To date, no explicit results have been obtained for stochastic c, and no new results of any form have appeared since the 1970’s. In this paper, we obtain the first results for stochastic c, and new explicit results if b an c are stochastic vectors with an exponential, gamma, uniform, or triangle distribution. A transformation is utilized that greatly reduces computational time.
文摘为了充分利用DTN中各节点资源,减少Epidemic Routing、spray and wait中不区分各节点资源不同,提出了一个基于节点密度、节点运动速度、生存期、节点缓存大小诸多因素,来进行消息转发的算法multi。通过仿真实验表明,multi算法较Epidemic Routing、spray and wait算法在消息成功传输率、平均延迟、网络开销、消息在缓存中滞留的时间上都有明显改善。
文摘机会网络利用节点移动形成的通信机会来逐步传输消息.然而当机会网络应用在海洋上时,由于海域广阔,节点分布稀疏,所以船舶之间相遇通信的概率较低,同时由于船速较慢,固定航道,传统机会网络路由协议执行效率不高.利用船舶位置信息和航行方向等,结合插值算法预测节点未来可能到达的位置,并对Spray and Wait协议改进,从而增加数据传递到目的船舶的可能性和效率,提高了船舶机会网络连通性.最后,通过仿真实验与目前比较流行的机会网络路由协议进行比较,取得较好的实验结果.
