上市首日“破发”股票长期表现更差吗?

以2009年7月至2012年5月间上市发行股票为样本,采用随机前沿模型进行定价分析,以新股发行定价类型,首日发行抑价率正负进行分类。选取折价发行且上市首日"破发"(即首日收盘价低于发行价)公司样本,将其与溢价发行且上市首日未"破发"公司样本,按照"行业-收入规模"标准进行样本配对,计算两组公司上市后1~5年买入与持有收益(BHAR)并进行差异性检验。结果表明:新股上市后前三年均表现不佳,折价发行且首日"破发"的股票在上市后前两年表现更差。这为新股定价与长期表现相关研究提供了新的实证。

新股“破发”的原因与意义——基于华锐风电的分析

在各国的资本市场中,新股发行均存在明显的低定价现象。我国资本市场尚处于发展期,并不完备,IPO抑价(即一级市场价格低于二级市场价格)程度较之国外更为严重,因此,一级市场往往被认为是"无风险"市场,通过"打新"获取无风险收益是许多投资者乐此不疲的投资方式。而大量申购新股的资金被冻结,巨额资金在银行与一级市场之间无序流动,导致证券市场配置资源的功能失效。然而,随着IPO定价的市场机制逐步建立,"破发"现象也不断出现,IPO"抑价"变"溢价"。本文以华锐风电为例,对新股"破发"产生的原因及其对证券市场造成的影响和启示进行探讨。

Damage and fracture behavior and spatio-temporal evolution of acoustic emission of sandstone before and after laser radiation

Laser technology holds significant promise for enhancing rock-breaking efficiency.Experimental investigations were carried out on sandstone subjected to laser radiation,aiming to elucidate its response mechanism to such radiation.The uniaxial compressive strength of sandstone notably decreases by 22.1%–54.7%following exposure to a 750 W laser for 30 s,indicating a substantial weakening effect.Furthermore,the elastic modulus and Poisson ratio of sandstone exhibit an average decrease of 33.7%and 25.9%,respectively.Simultaneously,laser radiation reduces the brittleness of sandstone,increases the dissipated energy proportion,and shifts the failure mode from tensile to tension-shear composite failure.Following laser radiation,both the number and energy of acoustic emission events in the sandstone register a substantial increase,with a more dispersed distribution of these events.In summary,laser radiation induces notable damage to the mechanical properties of sandstone,leading to a substantial decrease in elastic energy storage capacity.Laser rock breaking technology is expected to be applied in hard rock breaking engineering to significantly reduce the difficulty of rock breaking and improve rock breaking efficiency.

Strength and damage evolution mechanism of rock mass with holes under cyclic loading

The damage and failure law of rock mass with holes is of great significance to the stability control of roadways. This study investigates the mechanical properties and failure modes of porous rock masses under cyclic loading, elucidates the acoustic emission (AE) characteristics and their spatial evolution, and establishes the interrelation among AE, stress, strain, time, and cumulative damage. The results reveal that the rock mass with holes and the intact rock mass show softening and hardening characteristics after cyclic loading. The plastic strain of the rock mass with holes is smaller than that of the intact rock mass, and the stress −strain curve shows hysteresis characteristics. Under uniaxial compression, the pore-bearing rock mass shows the characteristics of higher ringing count, AE energy, b-value peak, and more cumulative ringing count in the failure stage, while it shows lower characteristics under cyclic action. At the initial stage of loading, compared with the intact rock mass, the pore-containing rock mass shows the characteristics of a low b-value. The AE positioning and cumulative damage percentage are larger, and the AE positioning is denser around the hole. The specimen with holes is mainly shear failure, and the complete specimen is mainly tensile shear failure.

Failure properties of rocks in true triaxial unloading compressive test

Slabbing failure often occurs in the surround rock near a deep underground excavation. The mechanism of slabbing failure is still unclear. In order to reveal the influence of the intermediate principal stress （σ2） on slabbing failure, true triaxial unloading compressive test was carried out based on the stress path of the underground engineering excavation, i.e., unloading the minimum principal stress （σ3）, keeping σ2, increasing the maximum principal stress （σ1）. The initiation and the propagation of slabbing fracture in rock specimens were identified by examining the acoustic emission （AE） and the infrared radiation characterization. The test results show that the failure modes of the granite and red sandstone specimens are changed from shear to slabbing with the increase of σ2. The AE characteristic of rock specimen under low σ2 is swarm type which is the main shock type under high σ2. The infrared radiation properties of rock specimen under different σ2 are also different. The temperature change area is just along the shear fracture such as the uniaxial compression. With the increase of σ2, the temperature change area is planar of rock specimen which proofs that the failure mode of rock specimen turns into slabbing.

Relationship between Vascular Elasticity and Spontaneous Rupture of Hepatocellular Carcinoma

Objective Spontaneous rupture of hepatocellular carcinoma (HCC) is common in Asia and Africa with unclear mechanism. In our previous study, we found that the deposition of immune complex on vascular wall and vascular injury were related to the HCC rupture. In this study, the structure of elastin around the small artery was deeply investigated to confirm our previous study. Methods Immunohistochemical technique and transmission electron microscopy were used to study 23 specimens from ruptured HCC and 30 cases of nonruptured HCC. Results The layer of elastin around the vascular wall was significant thicker in patients with ruptured HCC than that in nonruptured HCC. The proliferation of elastin, abnormal distribution of neutrophil elastase and degradation of collagen fibril were predominantly present in the specimens from ruptured HCC. The phenomenon of electron—dense deposit in the elastic lamina that represented the deposition of immune complex, and the signs of infiltrated neutrophils from bloodstream into the vascular wall that caused the vascular injury, also can be found in ruptured HCC. Since the damaged vessels could become stiff and weak, which would more prone to be splitting and results in hemorrhage and the rupture of HCC, we postulated that the preexisting of immune complex deposition and vascular injury may be relate to the ruptured HCC. Conclusion The vascular injury caused by immune complex deposition might relate to ruptured HCC. Key words hepatocellular carcinoma - rupture - elastin - elastase

Modeling of rock failure based on physical cellular automata

To analyze the effects of heterogeneous material characteristics on rock failure,a micro-heterogeneous physical cellular automata （Mh-PCA） model is introduced according to the cellular automata theory from a general power view.In this model,the neighbor is the Moore pattern and the Weibull distribution is adopted to simulate the rock heterogeneousness.Using this model,the evolvements and acoustic emission of rock failure are simulated for four materials of different degree of homogeneousness （m＝1,5,10,15）.The results show that the heterogeneous characteristic has a great effect on the rock failure,the more the homogeneousness,the fewer the crack branches and the more concentrated acoustic emissions.The physical cellular automata theory gives a new idea for studying rock failure.

Effects of Different Treatment Methods on Germination Rate of Hard Seeds of Wild Lotus corniculatus L

Birdsfoot trefoil （Lotus corniculatus L.） is high in nutritional value and adapted to slightly acidic, droughty, infertile, or wet soils. However, the impermeable seed coat restricts water imbibition and results in poor seed germination and subse- quent stand establishment. The aim of this study was to identify the dormancy mechanism of Birdsfoot trefoil seeds, and investigate the suitable pretreatment to overcome the poor seed germination. Germination behavior was characterized by using the final germination percentage and the mean germination time. The results indicated that coat thickness of dormant seeds was significant larger. The average hard seed rate was up to 92.3%. It was found that mechanical scarification, chemi- cal scarification with concentrated sulfuric acid （98% H_2SO_4）, and gibberellic acid soaking following freezing below zero temperature were effective in reducing hard- seededness and lead to increases of seed germination.

Liver Resection for Spontaneous Rupture of Primary Hepatocellular Carcinoma

Objective To study the effect of liver resection for spontaneous rupture of primary hepatocellulal carcinoma (PHCC). Methods The clinical data of 12 patients with ruptured PHCC treated by liver resection in Xiangya Hospital since 1970 were analyzed retrospectively. Results There were 10 males and 2 females with mean age of 42 (ranged 22–65) years in this series. Of the 12 patients, 11 underwent emergent hepatectomy and one 2-stage hepatectomy, including left segmental liver resection in 6 patients, left median lobectomy in 1, left hemihepatectomy in 1, partial right hepatectomy in 2, and tumor resection in 2. There was no operative death in 11 patients with liver function in grade A of Child-Paugh classification, but 1 patient with grade B liver function died of liver failure after operation. The operative mortality was 8.3%. In 11 survived patients, the postoperative median survival time was 16.5 months. The 1?, 3?, 5-year survival rate was 72.7%, 18.2%, 9.1% respectively; among them one patient has been alive free of the tumor for 25 years and 9 months. Conclusion Liver resection is the best treatment for ruptured PHCC when possible, which can result in long survival time. Key words liver resection - spontaneous ruptare - primary hepatocellular carcinoma

On-Line Monitoring of Cutting Tool Fracture & Wear

A technique of detecting cutting tool fracture and ultimate wear by si- multaneously monitoring both the spindle motor current and cutting process related acoustic emission(AE)in the cutting process is reported.The technique can detect breakage of drills having diameter over 0.8mm,turning cutter crack of area over 0.2mm,and the ultimate wear.The principle,system construction,experimental method and result of the technique are discussed.The ratio of success in detection approaches 96% or higher.

Spontaneous rupture of hepatic epithelioid hemangioendothelioma: A case report

Hepatic epithelioid hemangioendothelioma(HEH) is a rare tumor of vascular endothelial origin. Spontaneous rupture of HEH is a life-threatening complication and is extremely rare. HEH has variable malignant potential, and the clinical diagnosis remains challenging. Here we report a case of HEH with spontaneous rupture. A 44-year-old man presented with constant cutting pains over the right upper abdomen after eating. He had hemoptysis 11 d previously. Diagnostic abdominal puncture demonstrated active bleeding. Chest and abdominal computer tomography scan showed multiple ground-glass nodules over the lungs, multiple low-density intrahepatic nodules and massive hemorrhage. Transcatheter arterial embolization and exploratory laparotomy were performed and subsequent immunohistochemical examination confirmed a diagnosis of HEH.

Analysis of key technologies and development of integrated digital processing system for cast blasting design

Casting blast can greatly reduce the stripping cost and improve the production capacity of opencast coal mines. Key technologies including high bench blasting, inclined hole, millisecond blasting, pre-splitting blasting and casting blast parameters determination which have influence on the effect of casting blast have been researched with the combination of the ballistic theory and experience in mines. The integrated digital processing system of casting blast was developed in order to simplify the design process of casting blast, improve working efficiency and veracity of design result and comprehensively adopt the software programming method and the theory of casting blast. This system has achieved five functions, namely, the 3D visualization graphics management, the intelligent management of geological information, the intelligent design of casting blast, the analysis and prediction of the blasting effect and the automatic output of the design results. Long-term application in opencast coal mines has shown that research results can not only reduce the specific explosive consumption and improve the blasting effect, but also have high value of popularization and application.

Spontaneous rupture of a hepatic hydatid cyst into the peritoneum causing only mild abdominal pain:A case report

Hydatid disease is an endemic disease in certain areas of the world. It is located mostly in the liver. Spontaneous rupture of the hydatid cyst into the peritoneum is a rare condition, which is accompanied by serious morbidity and mortality generally. We present herein a case with a spontaneous rupture of a hepatic hidatid disease into the peritoneum without any serious symptoms. A 15-year- old boy was admitted to the emergency room with a mild abdominal pain lasting for a day. Physical examination revealed only mild abdominal tenderness. There was no history of trauma or complaints related to hydatid diseases. Ultrasonography showed a large amount of free fluid and a cystic lesion with irregular borders in the liver. He was operated on. Postoperative albendazol therapy was given for 2 mo. No recurrence or secondary hydatidosis was seen on CT investigation in the 3^th, 6^th and 12^th mo following surgery.

Damage process and performance of PVA fiber-reinforced alkali-activated slag mortar plate under bending

The effects of unoiled polyvinyl alcohol(PVA)fiber with four different volume fractions of 0%,1.0%,1.5%and 2.0%on the bending properties of alkali-activated slag(AAS)mortar plates were studied.Meanwhile,the acoustic emission(AE)technique and a high-speed camera were utilized to detect the crack development over the complete damage process,and the scanning electronic microscopy(SEM)was used to observe the fiber-matrix interface.Test results show that PVA fibers play a significant role in the toughness improvement of AAS plates.However,the enhancing effect of PVA fibers on the bending behaviour of AAS plates at 120 d is not as remarkable as at early ages.It is observed that the failure process of the PVA fiber-reinforced alkali-activated slag plate can be divided into three stages:elastic stage,main crack formation stage and post-peak load stage.Observations on the fracture surface of specimens indicate that the deterioration process of specimens under bending changed from fiber pull-out at 3 and 28 d to fiber fracture at 120 d.

Failure modes and slabbing mechanisms of hard rock with different height-to-width ratios under uniaxial compression

To determine the relationship between slabbing failure and the specimen height-to-width(H/W)ratio and to analyze the conditions,characteristics,and mechanism of slabbing failure in the laboratory,uniaxial compression tests were conducted using six groups of granite specimens.The entire failure process was recorded using strain gauges and high-speed cameras.The initiation and propagation of fractures in specimens were identified by analyzing the monitoring results of stress,strain,and acoustic emission.The experimental results show that changes in the specimen H/W ratio can transform the macro failure mode.When the H/W ratio is reduced to 0.5,the macro failure mode is dominated by slabbing.Low load-bearing ability is observed in specimens with slabbing failure,and the slabbing fractures are approximately parallel to the loading direction.Moreover,the fracture propagation characteristics and acoustic emission signals of slabbing failure specimens show typical tensile failure characteristics,indicating that slabbing failure is essentially a special tensile failure.

Spontaneous liver rupture in hypereosinophilic syndrome:A rare but fatal complication

We report a rare case of spontaneous liver rupture in a patient with hypereosinophilic syndrome(HES),of which the diagnosis was delayed,resulting in a fatal outcome.The diagnostic criteria and treatment of HES with hepatic involvement were reviewed.The possible cause of spontaneous liver rupture in HES and its management were also discussed.To our knowledge,this is the fi rst case report of spontaneous liver rupture in HES.We emphasized the need of a high index of suspicion in diagnosing HES,so that early treatment could be initiated.

Exponential decay law of acoustic emission and microseismic activities caused by disturbances associated with multilevel loading and mining blast

To investigate decay law of acoustic emission and microseismic activities caused by disturbances associated with multilevel loading and mining blast,a new exponential decay(ED)law was proposed.The results show that the micro-fracture activity decay law after multistage stress loading and blasting disturbance conforms to the ED model,in which the sum of A and n represents the number of initial micro-fracture events,and n represents the level of background micro-fracture events.The ED model can describe the number of initial micro-fracture events with a deviation less than 10%.The ED model outperforms the traditional aftershock models in describing the micro-fracture event decay law in the three cases considered.The ED model can provide a reference for selecting the blasting interval in mines,which is of great significance to maintain the stability of the surrounding rock and ensure safe production in metal mines.

Current treatment of rectovaginal fistula in Crohn's disease

Rectovaginal fistula(RVF) continues to be the most difficult perianal manifestation of Crohn's disease to treat.This devastating and disabling complication has a significant impact on patients' quality of life and presents unique management challenges.Current therapeutic approaches include many medical therapeutics and surgical treatments with a wide range of success rates reported.However,current evidence is lacking to support any recommendation.The choice of repair depends on various patient and disease factors and basic surgical tenets.In this article,we review the current options to consider in the treatment of Crohn's-related RVF,and try to evaluate their effects on fistulae closure and quality of life.

Long-term survival for spontaneous rupture of hepatocellular carcinoma treated with hepatectomy

Objective- To determine the prognostic factors of ruptured hepatocellular carcinoma （HCC） and report the management of patients with spontaneous rupture of HCC in a single center during a 5-year period and to evaluate one-stage hepatectomy Methods- A series of 4,209 patients with HCC were collected at Eastern Hepatobiliary Surgery Hospital from April 2002 to November 2006, of whom 200 patients （4.8%） with ruptured HCC were studied retrospectively regarding their clinical characteristics and prognostic factors. The one-stage therapeutic approach to manage ruptured HCC consisted of initial management by conservative method, transarterial embolization （TAE） or surgical hepatectomy. Results of various treatments were evaluated and compared in the randomly selected 202 patients with no history of rupture during the same study period. Results： A total of 200 patients with spontaneous rupture of HCC were studied who underwent surgical treatment （n=105）, TAE 33 and conservative treatment （ConT 62）. A multivariate analysis using the Cox hazard regression model （including all the patients n=200） identified surgical hepatectomy as the only independent factor determining a relatively long survival period （P〈0.0001） On the other hand, in a further analysis of the patients in whom surgical hepatectomy was successfully performed （n=105）, which identified a maximum tumor size exceeding 6 cm as significant determinants of a poor 12-month （P=0.036）, and a multivariate analysis did not identify as any inverse independent factor determining relatively long-term survival, only a maximum tumor size exceeding 6 cm exhibited a tendency toward being a determinant factor （P=0.083）. Conelusionz Considering the high propensity to spontaneous rupture, as long as preoperatively clinical evaluation meet surgery requirements, elective one-stage hepatectomy for patients with ruptured HCC is the first treatment option. Prolonged survival could be achieved in selected patients with hepatic resection, although the survival results were inferior to those of the patients who did not have the complication of rupture

Detonation initiated disintegration of coal particle due to the maxi- mum strain energy theory

Fragmentation behaviour of coal particles subjected to detonation wave is being studied. Detonation wave is initiated by a plasma cartridge at one end of a detonation tube. Coal particles are subjected to a shock whose temperature depends on the Mach number of the detonation wave. Temperature shock is found to generate thermal stresses which may fragment the coal particles. A non-dimensional mathematical model for the heat transfer process in the coal particle is proposed. Thermal stresses are calculated at various times and radii while maximum strain energy theory is used to understand the failure behavior viz., the time, temperature and location of fracture. A physical model for coal particle fragmentation when subjected to detonation wave is also proposed. The study suggests that detonation combustion of coal is qualitatively different from conventional method.