Localized Technological Externalities and the Geographical Distribution of Firms

LEM Working Paper - 2008/1

Evolution and Market Behavior with Endogenous Investment Rules

LEM - Working Paper 2010/2

Bounded rationality and heterogeneity in economic dynamic models

outline Economic phenomena are characterized by a strong mutual dependence between the choices of economic actors, e.g. individual consumers or firms, and the economic envi-ronment in which these choices are made and evaluated. The origin of this dependence lies in the fact that the economic environment is formed by the aggregation of all individ-ual choices, while at the same time individual choices are affected by the overall economic environment. In order to clarify the nature of this dependence, consider the following examples which will be recurrent throughout this thesis. In a market of a perishable consumption good, firms have to decide today how much to produce to supply to the market tomorrow. On the one hand, firms base their production decision upon tomorrow’s expected profits. On the other hand, tomorrow’s profits will depend on the total amount firms produce. In fact, given consumer demand, profits are a function of market clearing prices, which depend on total supply. Financial markets are another well-known example of this mutual dependence between choices and environment. The demand of investors for an asset is driven by expected future returns, while at the same time asset returns are determined, through realized asset prices, by investors ’ demand. Another example, with the advantage of appealing to everyone’s experience, is the El Farol problem proposed by Arthur (1994). El Farol is a bar where a live music show takes place on a fixed day, say Thursday, every week. There are 100 people who would like to go to the bar on Thursday evening, but the El Farol bar is not big enough for all of them. In fact, the bar is too crowded when there are more than 60 people. Each Thursday evening everyone decides whether to go to the bar or not. Each decision maker is directly influencing the number of agents present at the bar, and at the same time, since that number affects his or her utility, expectations about the number of agents present at the bar influence each individual

A challenging hernia: primary venous aneurysm of the proximal saphenous vein

Introduction: Primary venous aneurysm is a rare, but essential consideration in the differential diagnosis of an inguinal and femoral hernia. Methods: We report a case of a 43-year-old man who was referred for evaluation and treatment of a femoral hernia. Results: The patient presented with a 3-month history of an asymptomatic tumor on his right upper inner thigh. Physical examination noted a non-tender, non-indurated tumor. Conclusion: Surgical exploration demonstrated a primary venous aneurysm of the proximal saphenous vei

Laparoscopy for small bowel obstruction: the reason for conversion matters

Background: Although laparoscopy is associated with reduced hospital stay, early recovery, and decreased morbidity compared with open surgery, it is not well established for the treatment of small bowel obstruction (SBO). Methods: This study analyzed a prospective nationwide database of the Swiss Association of Laparoscopic and Thoracoscopic Surgery. Results: From 1995 to 2006, 537 patients underwent laparoscopy for SBO. Matted adhesions were the main cause of obstruction (62.6%). Intraoperative complications occurred for 9.5% of the patients. Postoperative morbidity was 14% and mortality 0.6%. Within 30days, 13 patients (2.4%) were readmitted because of early recurrence or complications. The conversion rate was 32.4%. The conversions resulted from inability to visualize the site of obstruction or matted adhesions (53.4%), intraoperative complications (21.3%), and small target incisions for resection (25.3%). Emergency operations were associated with higher conversion rates (43.6% vs 19.8%; p<0.001) but not with significantly more postoperative complications (15.2% vs 11.9%; p=0.17). Intraoperative complications and conversion were associated with significantly increased postoperative morbidity (39.2% vs 11.3%; p<0.001 and 24.7% vs 8.3%; p<0.001, respectively). Reactive conversion due to intraoperative complications was associated with the highest postoperative complication rate (48.6%). Morbidity for preemptive conversion due to impaired visualization/matted adhesions or a small-target incision was significantly lower (20% and 26.1%; p=0.02 and p<0.001, respectively). American Society of Anesthesiology (ASA) scores higher than 2 also were associated with postoperative morbidity (p<0.001). However, multivariate regression analysis showed that reactive conversion was the only independent risk factor for postoperative morbidity (p<0.001; odds ratio, 3.97; 95% confidence interval, 1.83-8.64). Conclusions: Laparoscopic management of SBO is feasible with acceptable morbidity and low mortality but with a considerable conversion rate. Early conversion is recommended to reduce postoperative morbidit

Long-term follow-up after combined fissurectomy and Botox injection for chronic anal fissures

Background and aims: Chronic anal fissures are difficult to treat. The aim of this retrospective study was to determine the outcome of combined fissurectomy and injection of botulinum toxin Type A (BT). Materials and methods: Between January 2001 and August 2004, 40 patients (21 women), median age 37years (range 18 to 57), underwent fissurectomy and BT injection. Fissurectomy was performed followed by injection of 10U of BT into the internal anal sphincter on both sides of the fissure. All patients were clinically checked 6weeks after the operation. At 1year, patients were sent a detailed questionnaire regarding symptoms, recurrence and further treatment for evaluation of long-term results. Results/findings: At 6weeks, 38 patients (95%) were free of symptoms. No adverse effects were detected. The response rate of questionnaires was 93%; the median follow-up was 1year (range 0.9 to 1.6). In the long-term, a recurrence was found in four patients. These patients were treated successfully with repeated fissurectomy and BT injections and salvage procedures, respectively. Overall, the success rate of combined fissurectomy and BT injection was 79%. Interpretation/conclusion: Combined fissurectomy and Botox injection for chronic anal fissure is an excellent and safe procedure with low morbidity and a high healing rat

Long-term follow-up after combined fissurectomy and Botox injection for chronic anal fissures

Background and aims: Chronic anal fissures are difficult to treat. The aim of this retrospective study was to determine the outcome of combined fissurectomy and injection of botulinum toxin Type A (BT). Materials and methods: Between January 2001 and August 2004, 40 patients (21 women), median age 37years (range 18 to 57), underwent fissurectomy and BT injection. Fissurectomy was performed followed by injection of 10U of BT into the internal anal sphincter on both sides of the fissure. All patients were clinically checked 6weeks after the operation. At 1year, patients were sent a detailed questionnaire regarding symptoms, recurrence and further treatment for evaluation of long-term results. Results/findings: At 6weeks, 38 patients (95%) were free of symptoms. No adverse effects were detected. The response rate of questionnaires was 93%; the median follow-up was 1year (range 0.9 to 1.6). In the long-term, a recurrence was found in four patients. These patients were treated successfully with repeated fissurectomy and BT injections and salvage procedures, respectively. Overall, the success rate of combined fissurectomy and BT injection was 79%. Interpretation/conclusion: Combined fissurectomy and Botox injection for chronic anal fissure is an excellent and safe procedure with low morbidity and a high healing rat

Distributions of Sharks across a Continental Shelf in the Northern Gulf of Mexico

Declines in shark populations have sparked researchers and fishery managers to investigate more prudent approaches to the conservation of these fish. As managers strive to improve data collection for stock assessment, fisheries-independent surveys have expanded to include data-deficient areas such as coastal regions. To that end, a catch series from a nearshore survey off Alabama was combined with data from a concurrent offshore survey with identical methodology to examine the depth use of sharks across the continental shelf (2–366 m). The combined data set contained 22 species of sharks collected from 1995 to 2008: 21 species in the offshore data set (1995–2008) and 12 species in the nearshore data set (2006–2008). Depth was a significant factor determining species’ distributions, primarily for Atlantic sharpnose Rhizoprionodon terraenovae, blacknose Carcharhinus acronotus, and blacktip C. limbatus sharks. Blacknose sharks had the highest catch per unit effort (CPUE) in the middepth stratum (10–30 m), blacktip sharks had consistently higher CPUE in the shallow depth stratum (,10 m), and Atlantic sharpnose sharks showed high abundance throughout both the shallow and mid-depth strata. Length frequency and sex ratio analyses suggest that Atlantic sharpnose and blacknose sharks are using waters greater than 30 m deep for parturition, whereas adult blacktip sharks are probably using shallow waters for parturition. Our abundance patterns illustrate a continuum of depth use across the inner continental shelf. Surveys that do not encompass the entirety of this ecosystem fail to accurately characterize the distributions of these important predators

Implementing mass rearing of trissolcus japonicus (Hymenoptera: Scelionidae) on cold-stored host eggs

Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), a pest of Asian origin, has been causing severe damage to Italian agriculture. The application of classical biological control by the release of Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae), an exotic egg parasitoid, appears to be one promising solution. In Italy, releases of T. japonicus in the field were authorized in 2020. In this study, some parameters that could influence the rearing of T. japonicus in insectaries were investigated. A significantly higher production of progeny was observed on host eggs stored at 6◦C (86.5%) compared to −24◦C (48.8%) for up to two months prior to exposure to parasitism. There were no significant differences in progeny production from single females in a vial provided with only one egg mass (83.2%) or 10 females inside a cage with 6 egg masses (83.9%). The exposure of parasitoids to refrigerated (6◦C) egg masses of H. halys for 72 h led to a significantly higher production of progeny (62.1%) compared to shorter exposures for 48 (44.0%) or 24 h (37.1%). A decline in production of progeny by the same female was detected between the first (62.1%) and the second parasitization (41.3%). Adult parasitoids stored at 16◦C for up to 90 days had an 87.1% survival rate, but a significant decrease in progeny production was detected. These parameters could be adjusted when rearing T. japonicus for specific aims such as the production of individuals for field release or colony maintenance

Age, Growth, and Mortality of Atlantic Tripletail in the North-Central Gulf of Mexico

In the southeastern USA and the Gulf of Mexico (GOM), Atlantic Tripletail Lobotes surinamensis are increasingly targeted by recreational anglers, indicating that stock status should be assessed. A critical need for such assessments is age-specific data; however, previous studies have drawn conflicting conclusions regarding the most appropriate structure for aging. Moreover, growth parameters and mortality rates for GOM Atlantic Tripletail are unknown. Therefore, the goals of this study were to (1) evaluate sagittal otoliths and first dorsal spines as aging structures; (2) model combined and sex-specific growth; and (3) estimate mortality rates for GOM Atlantic Tripletail. From 2012 to 2019, Atlantic Tripletail (N = 230, including a near-record-size specimen) were collected from the north-central GOM via hook and line and were aged using otoliths and first dorsal spines. Total length ranged from 212 to 940 mm, and age ranged from 0.07 to 5.27 years. Otoliths produced higher percent agreement (95.0%) and lower average percent error (3.0%) between readers compared to spines (82.9% and 6.5%, respectively). The von Bertalanffy growth parameters differed slightly between the otolith-based data (mean asymptotic length [L∞] = 762.42 mm, Brody growth rate coefficient [k] = 0.69 year−1, and hypothetical age at which length equals zero [t0] = −0.58 year) and spine-based data (L∞ = 718.83 mm, k = 0.79 year−1, and t0 = −0.56 year). For both otolith- and spine-based sex-specific data, the best-fitting version of the von Bertalanffy growth function permitted L∞ to vary by sex. Chapman– Robson estimates of instantaneous total mortality rate and total annual mortality rate were 1.15 and 68.66%, respectively. Based on empirical, life history-based methods, the instantaneous natural mortality rate was estimated at 0.75–0.97 and the instantaneous fishing mortality rate was estimated at 0.18–0.45, suggesting low levels of exploitation. These growth parameters and mortality estimates will provide information for future stock assessments, thereby ensuring sustainability of the GOM stock of Atlantic Tripletail