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The current perspective of the PA 1957 gas well pillar study and its implications for longwall gas well pillars

International Journal of Mining Science and Technology 2021年第1期31卷 117-126页

作者： Peter Zhang daniel su Chris Mark CDC NIOSH Pittsburgh Mining Research DivisionPittsburghPA 15236USA Mine Safety and Health Administration PittsburghPA 15217USA

Many states rely upon the Pennsylvania 1957 Gas Well Pillar Study to evaluate the coal barrier surrounding gas *** study included 77 gas well failure cases that occurred in the Pittsburgh and Freeport coal seams over a 25-year *** the time,coal was mined using the room-and-pillar mining method with full or partial pillar recovery,and square or rectangle pillars surrounding the gas wells were left to protect the *** study provided guidelines for pillar sizes under different overburden depths up to 213 m(700 ft).The 1957 study has also been used to determine gas well pillar sizes in longwall mines since longwall mining began in the 1970 *** original study was developed for room-and-pillar mining and could be applied to gas wells in longwall chain pillars under shallow ***,under deep cover,severe deformations in gas wells have occurred in longwall chain ***,with a better understanding of coal pillar mechanics,new insight into subsidence movements induced by retreat mining,and advances in numerical modeling,it has become both critically important and feasible to evaluate the adequacy of the 1957 study for longwall gas well *** this paper,the data from the 1957 study is analyzed from a new perspective by considering various factors,including overburden depth,failure location,failure time,pillar safety factor(SF),and floor *** pillar SF and floor pressure are calculated by considering abutment pressure induced by full pillar recovery.A statistical analysis is performed to find correlations between various factors and helps identify the most significant factors for the stability of gas wells influenced by retreat *** analyzing the data from the 1957 study,the guidelines for gas well pillars in the 1957 study are evaluated for their adequacy for roomand-pillar mining and their applicability to longwall *** modeling is used to model the stability of gas wells by quantifying the mining-induced s

关键词： Gas well pillar Pennsylvania 1957 gas well pillar study Room-and-pillar mining Longwall mining

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The retinal function imager and clinical applications

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Eye and Vision 2018年第1期5卷 191-195页

作者： daniel su sunir Garg The Retina Service of Wills Eye Hospital Mid Atlantic Retina840 Walnut StreetSuite 1020PhiladelphiaPA 19107USA

Background:The Retinal Function Imager(RFI)provides in vivo and noninvasive imaging of both the retinal structure and ***:The RFI can create capillary perfusion maps,measure blood flow velocity,and determine metabolic function including blood *** can aid clinical diagnosis as well as assess treatment response in several retinal vascular diseases including diabetic *** flow velocity abnormalities have also been implicated in disease such as age-related macular degeneration and require further *** with optical coherence tomography angiography,the RFI produces capillary maps of comparable image quality and wider field of view but it is unable to provide depth-resolved information and has longer image acquisition ***,functional imaging using blood oximetry has limited applications and additional research is ***:The RFI offers noninvasive,high-resolution imaging of retinal microvasculature by creating capillary perfusion *** addition,it is capable of measuring retinal blood velocity directly and performs functional imaging with retinal blood *** clinical applications are broad and additional research with functional imaging may potentially lead to diagnosis of diseases and their progression before anatomic abnormalities become evident,but longer image acquisition times may limit its clinical adoption.

关键词： Retinal function imager Retinal blood flow Blood flow velocity Oximetry Noninvasive imaging Retina

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Influence of longwall mining on the stability of gas wells in chain pillars

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International Journal of Mining Science and Technology 2020年第1期30卷 3-9页

作者： Peter Zhang Heather Dougherty daniel su Jack Trackemas Berk Tulu CDC NIOSH Pittsburgh Mining Research Division(PMRD)PittsburghPA 15236USA Department of Mining Engineering West Virginia UniversityMorgantownWV 26505USA

Longwall mining has a significant influence on gas wells located within longwall chain *** subsidence and abutment pressure induced by longwall mining can cause excessive stresses and deformations in gas well *** the gas well casings are compromised or ruptured,natural gas could migrate into the mine workings,potentially causing a fire or *** the current safety regulations,the gas wells in the chain pillars have to be either plugged or protected by adequate coal *** current regulations for gas well pillar design are based on the 1957 Pennsylvania gas well pillar *** study provided guidelines for gas well pillars by considering their support area and overburden depth as well as the location of the gas wells within the *** the guidelines were developed for room-andpillar mining under shallow cover,they are no longer applicable to modern longwall coal mining,particularly,under deep *** well casing of failures have occurred even though the chain pillars for the gas wells met the requirements by the 1957 *** study,conducted by the National Institute for Occupational Safety and Health(NIOSH),presents seven cases of conventional gas wells penetrating through longwall chain pillars in the Pittsburgh Coal *** study results indicate that overburden depth and pillar size are not the only determining factors for gas well *** other important factors include subsurface ground movement,overburden geology,weak floor,as well as the type of the construction of gas *** modeling was used to model abutment pressure,subsurface deformations,and the response of gas well *** study demonstrated that numerical models are able to predict with reasonable accuracy the subsurface deformations in the overburden above,within,and below the chain pillars,and the potential location and modes of gas well failures,thereby providing a more quantifiable approach to assess the stability of the gas wells in l

关键词： Longwall mining Gas well Chain pillar Casing stability

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Ground response to high horizontal stresses during longwall retreat and its implications for longwall headgate support

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International Journal of Mining Science and Technology 2019年第1期29卷 27-33页

作者： Peter Zhang Dave Gearhart Mark Van Dyke daniel su Essie Esterhuizen Berk Tulu NIOSH Pittsburgh Mining Research Division(PMRD) Department of Mining Engineering West Virginia University

Roof falls in longwall headgate can occur when weak roof and high horizontal stress are present. To prevent roof falls in the headgate under high horizontal stress, it is important to understand the ground response to high horizontal stress in the longwall headgate and the requirements for supplemental roof support. In this study, a longwall headgate under high horizontal stress was instrumented to monitor stress change in the pillars, deformations in the roof, and load in the cable bolts. The conditions in the headgate were monitored for about six months as the longwall face passed by the instrumented *** roof behavior in the headgate near the face was carefully observed during longwall *** modeling was performed to correlate the modeling results with underground observation and instrumentation data and to quantify the effect of high horizontal stress on roof stability in the longwall headgate. This paper discusses roof support requirements in the longwall headgate under high horizontal stress in regard to the pattern of supplemental cable bolts and the critical locations where additional supplemental support is necessary.

关键词： Longwall mining Longwall headgate High horizontal stress supplemental support

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Transitional geology and its effects on development and longwall mining in Pittsburgh Seam

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International Journal of Mining Science and Technology 2016年第1期26卷 31-37页

作者： Lu Jun Van Dyke Mark su daniel W.H. Hasenfus Greg Geomechanical Engineer Consol Energy Inc.

This paper presents the geologic and ground control challenges that were encountered by Consol Energy＇s coal mining operations in southwestem Pennsylvania, USA. Geologic encounters, such as sandstone- to-limestone geology transition, massive sandstone channels, shale channels, pyritic rich green claystone, laminated roof, and soft floor, have significantly impacted the development and longwall mining in Consol＇s Pittsburgh Seam coal mines. Experience from different mines shows that, in the sandstone-to-limestone geology transition zone, 1.83 m high-tension, fully-grouted primary bolts employed along with 4.88 m cen- ter cable bolts at every other strap greatly improved beam building and ensured proper anchorage into the competent roof. Hydraulic fracturing of the massive sandstone was often necessary to enhance caving of the massive sandstone behind the shields to relieve pressure at the face. The presence of soft floor coupled with presence of thick floor coal and deep cover, induced excessive headgate convergence during retreat of the first right hand longwall panel. In all, it is important to explore the roof and in-seam geology in detail to delineate normal and anomalous geologic conditions prior to and during development. With diligent geologic reconnaissance, geotechnical monitoring, and assessment, site-specific geotechnical solutions have been provided to mine operations to improve safety and productivity.

关键词： Coal miningGeology transition zoneGround controlRoof bolt

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Alpha-1 Antitrypsin Panniculitis:What’s New?

Alpha-1 Antitrypsin Panniculitis:What’s New?

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中华医学会第十二次全国皮肤性病学术会议

作者： W.P．daniel su Mayo Graduate School College of Medicine M.D.

Alpha-1 antitrypsin (AAT) is the major serum protease inhibitor of our body, a glycoprotein synthesized in the liver. Individuals who are deficient in AAT are at risk for developing panniculitis, anticytoplasmic neutrophilic antibody (C-ANCA)-positive vasculitis (Wegener’s granulomatosis), emphysema and liver cirrhosis. In AAT-deficient patients, panniculitis has been precipitated by cryotherapy, trauma, surgical debridement,

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27-gauge vitrectomy--an update on recent surgical outcomes

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Eye Science 2016年第4期31卷 211-213页

作者： daniel su Jean-Pierre Hubschman Stein Eye Institute University of California Los Angeles USA

The introduction of transconjunctival sutureless microincision vitrectomy surgery(MIVS)with 23-and25-gauge(23 and 25 G)instrumentation has virtually replaced the more antiquated 20-gauge equivalents,resulting in short... 详细信息

关键词：玻璃体手术切除术结膜

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SWEETS SYNDROME & PYODERMA GANGRENOsuM:A Clinicopathologic Connection

SWEETS SYNDROME & PYODERMA GANGRENOSUM:A Clinicopathologic C...

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中华医学会第14次全国皮肤性病学术年会

作者： W.P.daniel su Professor Mayo Medical School ConsultantMayo Clinic College of Medicine

In the skin biopsy of Sweet’s Syndrome & Pyoderma gangrenousm, neutrophilic infiltrate is usually a prominent feature. There is consideration of classifying them together as Neutrophilic Dermatosis. From the original de- scriptions, however, they are quite different in clinical appearance. Are they the same disease or separate en- tities?

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假肢手接受腔恒力挤压块设计

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医用生物力学 2016年第6期31卷 520-524页

作者：刘杰民 daniel su 桑元俊李祥罗云上海交通大学机械与动力工程学院机械系统与振动国家重点实验室上海200240

目的针对假肢手接受腔挤压模块的功能需求,设计一种恒力输出的挤压机构。方法根据正负弹簧刚度抵消获得恒力的工作原理,基于有限元分析软件ANSYS进行仿真拟合,测定弹簧片的弹性刚度系数,从而计算获得正刚度弹簧的弹性刚度系数,对加工组... 详细信息

目的针对假肢手接受腔挤压模块的功能需求,设计一种恒力输出的挤压机构。方法根据正负弹簧刚度抵消获得恒力的工作原理,基于有限元分析软件ANSYS进行仿真拟合,测定弹簧片的弹性刚度系数,从而计算获得正刚度弹簧的弹性刚度系数,对加工组装后的恒力挤压机构进行压力测试。结果恒力机构的仿真结果与实验结果一致,并且在3.5 mm行程范围内实现了2%的压力恒定性。结论实验证实了挤压单元的恒力特性,为今后的假肢手接受腔分时分区控制奠定了基础。

关键词：假肢接受腔恒力机构弹簧片有限元分析

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Risk factors for long COVID in children and adolescents:a systematic review and meta-analysis

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World Journal of Pediatrics 2024年第2期20卷 133-142页

作者： daniel G.Rayner Elaine Wang Cloris su Om D.Patel Stephanie Aleluya Alessandra Giglia Evelyn Zhu Maha Siddique Department of Health Research Methods Evidenceand ImpactFaculty of Health SciencesMcMaster University1280 Main St WHamiltonONL8S 4K1Canada Faculty of Health Sciences McMaster University1280 Main St WHamiltonON L8S 4K1Canada Faculty of Science McMaster University1280 Main St WHamiltonONL8S 4K1Canada

Background The long-term sequelae of COVID-19 in children and adolescents remain poorly understood and *** systematic review and meta-analysis sought to summarize the risk factors for long COVID in the pediatric *** We searched six databases from January 2020 to May 2023 for observational studies reporting on risk factors for long COVID or persistent symptoms those were present 12 or more weeks post-infection using multivariable regression *** registries,reference lists of included studies,and preprint servers were hand-searched for relevant ***-effects meta-analyses were conducted to pool odds ratios for each risk *** study risk of bias was rated using QUIPS,and the GRADE framework was used to assess the certainty of evidence for each unique *** Sixteen observational studies(N=46,262)were included,and 19 risk factors were amenable to *** moderate certainty in the evidence,age(per 2-year increase),allergic rhinitis,obesity,previous respiratory diseases,hospitalization,severe acute COVID-19,and symptomatic acute COVID-19 are probably associated with an increased risk of long *** sex,asthma,comorbidity,and heart diseases may be associated with an increased risk of long COVID,and Asian and Black races may be associated with a decreased risk of long *** did not observe any credible subgroup effects for any risk *** The current body of literature presents several compelling risk factors for the development of long COVID in the pediatric *** research is necessary to elucidate the pathophysiology of long COVID.

关键词： COVID-19 Long COVID Post-acute COVID-19 syndrome Pediatrics Risk factors

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