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Papers by JOSE ABOL CORREA
Proceedings of the forty-third annual ACM symposium on Theory of computing, 2011
We study coordination mechanisms aiming to minimize the weighted sum of completion times of jobs ... more We study coordination mechanisms aiming to minimize the weighted sum of completion times of jobs in the context of selfish scheduling problems. Our goal is to design local policies that achieve a good price of anarchy in the resulting equilibria for unrelated machine scheduling. To obtain these approximation bounds, we introduce a new technique that while conceptually simple, seems to be quite powerful. The method entails mapping strategy vectors into a carefully chosen inner product space; costs are shown to correspond to the norm in this space, and the Nash condition also has a simple description. With this structure in place, we are able to prove a number of results, as follows. First, we consider Smith's Rule, which orders the jobs on a machine in ascending processing time to weight ratio, and show that it achieves an approximation ratio of 4. We also demonstrate that this is the best possible for deterministic non-preemptive strongly local policies. Since Smith's Rule is always optimal for a given fixed assignment, this may seem unsurprising, but we then show that better approximation ratios can be obtained if either preemption or randomization is allowed. We prove that ProportionalSharing, a preemptive strongly local policy, achieves an approximation ratio of 2.618 for the weighted sum of completion times, and an approximation ratio of 2.5 in the unweighted case. We also observe that these bounds are tight. Next, we consider Rand, a natural nonpreemptive but randomized policy. We show that it achieves an approximation ratio of at most 2.13; moreover, if the sum of the weighted completion times is negligible compared to the cost of the optimal solution, this improves to π/2.
Mathematical Programming, 2014
A natural extension of the makespan minimization problem on unrelated machines is to allow jobs t... more A natural extension of the makespan minimization problem on unrelated machines is to allow jobs to be partially processed by different machines while incurring an arbitrary setup time. In this paper we present increasingly stronger
Jornal Brasileiro de Pneumologia, 2012
A previously healthy, 21-year-old female nonsmoker sought emergency room treatment complaining of... more A previously healthy, 21-year-old female nonsmoker sought emergency room treatment complaining of recent and progressive swelling of the face, neck, and chest (Figure ). The patient reported no pain, dyspnea, or dysphagia at admission. She reported a brief history of odynophagia in the previous week, when, during an episode of cough, she felt intense (dissecting) retrosternal pain, which subsided within a few minutes after its onset. After that episode, she had no symptoms other than the abovementioned swelling. Physical examination revealed extensive subcutaneous emphysema, which extended from the xiphoid process to the temporal muscle and involved the entire neck and face. Pulmonary percussion and auscultation revealed no abnormalities. Cardiac auscultation revealed the presence of Hamman's sign (crackles-as was the case in our patient-or bubbling sounds, synchronous with the heartbeat). Oral endoscopy revealed no abnormalities, and the remainder of the physical examination was normal. A CT scan of the skull, neck, and chest confirmed the presence of pneumomediastinum, pneumothorax (Figure ), and extensive soft tissue emphysema in the cervical region (Figure )involving the face, periorbital tissues, and temporal muscles (Figure )-as well as revealing the presence of pneumorrhachis (Figure ). From postadmission day two onward, the subcutaneous emphysema gradually improved. The patient received conservative treatment, including rest, unrestricted diet, and analgesia, if necessary. The results of routine laboratory tests, including blood workup and urinalysis, were normal. Follow-up chest X-rays revealed a sustained reduction in the abovementioned signs and symptoms. The patient remained under observation for another five days, being asymptomatic and showing nearly complete
Journal of Digital …, 1992
Postprocessing ofthe image data is an exciting capability of digital radiography that may improve... more Postprocessing ofthe image data is an exciting capability of digital radiography that may improve diagnostic performance. We present a new algorithm that selectively enhances edges and contrast in both lungs and mediastinum while minimally amplifying noise in chest images. Using different size kernels, two smoothed images are generated from the original chest image. The two regions of interest (lungs and mediastinum) are identified based on the distribution of pixel values in the image. A modified nonlinear unsharp mask subtraction technique is then applied. The resulting image has enhanced high-and middle-frequency information in the mediastinum without distorting lung parenchyma or significantly enhancing noise. We consider that the technique employed in this study could be suitable for routine use although its true effectiveness in improving diagnostic accuracy awaits observerperformance evaluation that is currently under way.
Proceedings of the forty-third annual ACM symposium on Theory of computing, 2011
We study coordination mechanisms aiming to minimize the weighted sum of completion times of jobs ... more We study coordination mechanisms aiming to minimize the weighted sum of completion times of jobs in the context of selfish scheduling problems. Our goal is to design local policies that achieve a good price of anarchy in the resulting equilibria for unrelated machine scheduling. To obtain these approximation bounds, we introduce a new technique that while conceptually simple, seems to be quite powerful. The method entails mapping strategy vectors into a carefully chosen inner product space; costs are shown to correspond to the norm in this space, and the Nash condition also has a simple description. With this structure in place, we are able to prove a number of results, as follows. First, we consider Smith's Rule, which orders the jobs on a machine in ascending processing time to weight ratio, and show that it achieves an approximation ratio of 4. We also demonstrate that this is the best possible for deterministic non-preemptive strongly local policies. Since Smith's Rule is always optimal for a given fixed assignment, this may seem unsurprising, but we then show that better approximation ratios can be obtained if either preemption or randomization is allowed. We prove that ProportionalSharing, a preemptive strongly local policy, achieves an approximation ratio of 2.618 for the weighted sum of completion times, and an approximation ratio of 2.5 in the unweighted case. We also observe that these bounds are tight. Next, we consider Rand, a natural nonpreemptive but randomized policy. We show that it achieves an approximation ratio of at most 2.13; moreover, if the sum of the weighted completion times is negligible compared to the cost of the optimal solution, this improves to π/2.
Mathematical Programming, 2014
A natural extension of the makespan minimization problem on unrelated machines is to allow jobs t... more A natural extension of the makespan minimization problem on unrelated machines is to allow jobs to be partially processed by different machines while incurring an arbitrary setup time. In this paper we present increasingly stronger
Jornal Brasileiro de Pneumologia, 2012
A previously healthy, 21-year-old female nonsmoker sought emergency room treatment complaining of... more A previously healthy, 21-year-old female nonsmoker sought emergency room treatment complaining of recent and progressive swelling of the face, neck, and chest (Figure ). The patient reported no pain, dyspnea, or dysphagia at admission. She reported a brief history of odynophagia in the previous week, when, during an episode of cough, she felt intense (dissecting) retrosternal pain, which subsided within a few minutes after its onset. After that episode, she had no symptoms other than the abovementioned swelling. Physical examination revealed extensive subcutaneous emphysema, which extended from the xiphoid process to the temporal muscle and involved the entire neck and face. Pulmonary percussion and auscultation revealed no abnormalities. Cardiac auscultation revealed the presence of Hamman's sign (crackles-as was the case in our patient-or bubbling sounds, synchronous with the heartbeat). Oral endoscopy revealed no abnormalities, and the remainder of the physical examination was normal. A CT scan of the skull, neck, and chest confirmed the presence of pneumomediastinum, pneumothorax (Figure ), and extensive soft tissue emphysema in the cervical region (Figure )involving the face, periorbital tissues, and temporal muscles (Figure )-as well as revealing the presence of pneumorrhachis (Figure ). From postadmission day two onward, the subcutaneous emphysema gradually improved. The patient received conservative treatment, including rest, unrestricted diet, and analgesia, if necessary. The results of routine laboratory tests, including blood workup and urinalysis, were normal. Follow-up chest X-rays revealed a sustained reduction in the abovementioned signs and symptoms. The patient remained under observation for another five days, being asymptomatic and showing nearly complete
Journal of Digital …, 1992
Postprocessing ofthe image data is an exciting capability of digital radiography that may improve... more Postprocessing ofthe image data is an exciting capability of digital radiography that may improve diagnostic performance. We present a new algorithm that selectively enhances edges and contrast in both lungs and mediastinum while minimally amplifying noise in chest images. Using different size kernels, two smoothed images are generated from the original chest image. The two regions of interest (lungs and mediastinum) are identified based on the distribution of pixel values in the image. A modified nonlinear unsharp mask subtraction technique is then applied. The resulting image has enhanced high-and middle-frequency information in the mediastinum without distorting lung parenchyma or significantly enhancing noise. We consider that the technique employed in this study could be suitable for routine use although its true effectiveness in improving diagnostic accuracy awaits observerperformance evaluation that is currently under way.