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Bruce Greenwald

Publications and source records attributed to Bruce Greenwald.

3 recordsLinked to original sources

All strategy is local.

The aim of strategy is to master a market environment by understanding and anticipating the actions of other economic agents, especially competitors. A firm that has some sort of competitive advantage-privileged access to customers, for instance--will have relatively few competitors to contend with, since potential competitors without an advantage, if they have their wits about them, will stay away. Thus, competitive advantages are actually barriers to entry and vice versa. In markets that are exposed, by contrast, competition is intense. If the incumbents have even brief success in earning greater than normal returns on investments, new entrants will swarm in to grab a share of the profits. Sooner or later, the additional competition will push returns as far down as the firms' costs of capital. For firms operating in such markets, the only choice is to forget about strategy and run the business as efficiently as possible. Barriers to entry are easier to maintain in a competitive arena that is "local", either in the geographic sense or in the sense of being limited to one product or a handful of related ones. The two most powerful competitive advantages-customer captivity and economies of scale-are more achievable and sustainable in circumscribed markets of this kind. Their opposites are the open markets and host of rivals that are features of globalization. Compapies entering such markets risk frittering away the advantages they secured on smaller playing fields.., Ifa company wants to grow but still obtain superior returns, the authors argue, the best strategy is to dominate a series of discrete but preferably contiguous markets and then expand only at their edges. WalMart's diminishing margins over the past 15 years are strong evidence of the danger of proceeding otherwise.

Commerce↗

Radiotherapy dose perturbation of metallic esophageal stents.

PURPOSE: Metallic esophageal stents frequently present during the treatment of esophageal cancer while using either external beam radiotherapy or brachytherapy. The dosimetric effects due to these metallic stents have not been reported. This work investigates these dose effects for various stent models presented during a radiotherapy procedure. METHODS AND MATERIALS: Two types of representative stent models, shell and ring stents, with various designs (e.g., composition and shell thickness or ring spacing), were studied. Three Monte Carlo code systems (EGS4/BEAM, EGSnrc/DOSRZnrc, and MCNP) were used to calculate the dose distributions for 6- and 15-MV external photon beams and for a (192)Ir brachytherapy source with and without a metallic esophageal stent in place. RESULTS: For a single external beam, a dose enhancement is generally observed in front of the stent (upstream) in the region within 4-mm distance of the stent surface. The enhancement at 0.5-mm distance from the stent surface can be as high as 20%. The dose behind the stent (downstream) is generally reduced. For a parallel-opposed pair (POP), a dose enhancement is always observed in the region within 3-mm distance of the stent surface. The enhancement at 0.5-mm distance from the stent surface can be as high as 10% for the 15-MV POP and 8% for the 6-MV POP. The dose effects depend on stent design (e.g., composition, thickness of shell stent, or ring spacing in ring stents). This dependence is reduced for a POP. In the case of the (192)Ir brachytherapy source, a dose enhancement is observed in the region within 1-mm distance from the stent surface. The dose enhancement is approximately 5% at 0.5-mm distance from the stent surface. CONCLUSION: The dose perturbations due to the presence of a metallic esophageal stent during the treatment of esophageal cancer while using either external beam radiotherapy or brachytherapy should be recognized. These perturbations result in an overdose in esophageal mucosa. The overdose is within 5%-10% at a depth of 0.5 mm in the esophageal wall.

Brachytherapy↗

Thoracoscopy/laparoscopy in the staging of esophageal cancer: Maryland experience.

Precise clinical staging of esophageal cancer before treatment is important. Thoracoscopic/laparoscopic (Ts/Ls) staging has been proposed as a promising staging method. This study was conducted to evaluate the potential benefits of Ts/Ls staging over conventional noninvasive clinical staging in patients with esophageal cancer. From 1991 to 1999, 111 patients with esophageal cancer underwent Ts/Ls staging by the University of Maryland Medical System. Pretreatment staging workup included computed tomography, magnetic resonance imaging, and esophageal ultrasonography, followed by Ts/Ls surgical staging. Thoracoscopy was successfully performed in 102 patients and was aborted in 4 patients because of pleural adhesions. Laparoscopy was successfully done in 76 patients and was aborted in 1 patient because of peritoneal adhesion. Sixty-seven patients had both Ts and Ls staging, whereas 35 patients and 9 patients, respectively, had only Ts or Ls staging. Thirteen of 19 patients with clinical T4 disease were downstaged to T3 disease, and 8 patients with clinical T3 disease were upstaged to T4 by Ts/Ls staging. No clinical T1-2 disease was found to be associated with local invasion (T4) by Ts/Ls. Forty-eight and 19 patients had mediastinal and celiac lymph node metastases clinically diagnosed, respectively. Nine (18.8%) and 12 (63.2%) of them were proved by Ts and Ls, respectively. An additional 5 and 16 patients were found to have unexpected mediastinal and celiac lymph node metastases, respectively, by Ts/Ls. Biopsy specimens of pleura, lung, or liver were obtained by Ts/Ls procedures in 17 patients because of suspicious findings of routine imaging studies or unexpected findings during the staging operation. Five patients were found to have distant metastasis, and the presence of metastases in others was excluded. The correlation between Ts/Ls staging and conventional noninvasive clinical staging in the diagnosis of T4 disease, mediastinal lymph node metastasis, celiac lymph node metastasis, and M1 disease was 18.8%, 14.5%, 25.5%, and 20.0%, respectively. Ts/Ls provides more accurate information for evaluating local invasion, lymph node metastasis, and distant metastasis. The poor correlation of staging diagnosis between Ts/Ls and conventional noninvasive clinical examinations suggests that the accuracy of current noninvasive clinical staging is questionable and needs to be improved.

Adenocarcinoma↗