Review of Proposed Stress-dilatancy Relationships and Plastic Potential Functions for Uncemented and Cemented Sands

Stress-dilatancy relationship or plastic potential function are crucial components of every elastoplastic constitutive model developed for sand or cemented sand. This is because the associated flow rule usually does not produce acceptable outcomes for sand or cemented sand. Many formulas have been introduced based on the experimental observations in conventional and advanced plasticity models in order to capture ratio of plastic volumetric strain increment to plastic deviatoric strain increment (i.e. dilatancy rate). Lack of an article that gathers these formulas is clear in the literature. Thus, this paper is an attempt to summarize plastic potentials and specially stress-dilatancy relations so far proposed for constitutive modelling of cohesionless and cemented sands. Stress-dilatancy relation is usually not the same under compression and extension conditions. Furthermore, it may also be different under loading and unloading conditions. Therefore, the focus in this paper mainly places on the proposed stress-dilatancy relations for compressive monotonic loading. Moreover because plastic potential function can be calculated by integration of stress-dilatancy relationship, more weight is allocated to stress-dilatancy relationship in this research

Distinct element modelling of the mechanical behaviour of intact rocks using voronoi tessellation model

This paper aims to study the mechanical behaviour and failure mechanism of intact rocks under different loading conditions using the grain based model implemented in the universal distinct element code (UDEC). The grain based numerical model is a powerful tool to investigate complicated micro-structural mechanical behaviour of rocks. In the UDEC grain based model, the intact material is simulated as assemblies of a number of polygonal blocks bonded together at their contact areas. To investigate the ability of such a numerical framework, uniaxial and triaxial compression tests as well as direct tensile test were simulated in UDEC and then the results were compared with the laboratory experiments undertaken on Hawkesbury sandstone. There was a good agreement between the experimental and numerical under different loading conditions. In order to investigate the effect of micro-properties of the grain based model, blocks and contacts, on the laboratory scale intact rocks, a set of parametric study was undertaken. The results from this analysis confirmed that the block size is an intrinsic characteristic of a model which has significant effects on the mechanical behaviour of the numerical models. Also, it was concluded that the cohesion and friction angle of contact surfaces control both uniaxial and triaxial compressive strengths. Finally, it was found that in the triaxial compression test, as the applied confining pressure increases, the effect of contact cohesion on the strength decreases while the effect of friction angle increases

The study of relationship between post dural puncture headache and hemodynamic fluctuation in patients undergoing spinal anesthesia

زمینه و هدف: به اعتقاد بسیاری از محققین علت بروز سردرد بعد از سوراخ شدن سخت شامه، نشت مایع مغزی نخاعی (CSF= Cerebrospinal Fluid) و کاهش فشار داخل مغز (ICP= Intracranial Pressure) است. تغییرات همودینامیک می تواند بر دینامیک CSF و وضعیت ICP تأثیر گذار باشد. مطالعه حاضر با هدف تعیین ارتباط نوسانات فشار خون، نبض، میزان مایع دریافتی و افدرین مصرفی با سردرد بعد از سوراخ شدن سخت شامه طراحی و اجراء شده است. روش بررسی: این مطالعه به صورت توصیفی - تحلیلی بر روی 95 بیمار با شکستگی ساق پا، نامزد بیهوشی نخاعی، با استفاده از سوزن نوعQuincke شماره 23 انجام شد. فشار خون و نبض در دقایق 1، 2، 4، 8 و 16 پس از انجام بیهوشی نخاعی اندازه گیری و ثبت شد. همچنین جمع مایع وریدی و افدرین دریافتی نیز محاسبه و ثبت گردید. سپس بروز، شدت (بر اساس پرسشنامه VAS=Visual Analog Scale) و مدت سردرد (روز) تا 5 روز بعد از انجام بیهوشی مورد بررسی قرار گرفت. در پایان ارتباط میزان بروز و شدت سردرد با نوسانات فشار خون، نبض، میزان مایع وریدی دریافتی و افدرین مصرفی با استفاده از آزمون های t مستقل و پیرسون مورد تجزیه و تحلیل قرار گرفت. یافته ها: از بیماران مورد مطالعه 3/33 دچار سردرد بعد از سوراخ شدن دورا شدند. میانگین شدت و طول مدت سردرد به ترتیب 11/2±83/5 (سانتیمتر) و 40/1±66/3 (روز) بود. بین درصد نوسانات فشارخون سیستول، دیاستول، متوسط شریانی، تعداد نبض، میزان مایع دریافتی و افدرین مصرفی با میزان بروز و شدت سردرد متعاقب بیهوشی نخاعی، رابطه معنی داری بدست نیامد. نتیجه گیری: عدم ارتباط معنی دار بین نوسانات همودینامیکی با میزان بروز و شدت سردرد می تواند نشان دهنده این موضوع باشد که علیرغم تأثیر عوامل همودینامیک بر دینامیک و وضعیت ICP، این عوامل احتمالاَ از قدرت کافی جهت تغییر در میزان نشت CSF از سوراخ دورا برخوردار نبوده و عامل تعیین کننده اصلی همان اندازه و شکل سوراخ ایجاد شده توسط سوزن های نخاعی است

Awareness of Ergonomics and its Relationship with the Prevalence of Musculoskeletal Disorders: a study on physiotherapists in Shiraz, Iran

Background: Ergonomics is a science dealing with human's physical and mental abilities and limitations, and inattention to this science leads to physical injuries among the staff and consequently affects the efficiency and productivity of the organisations. The aim of this study was to evaluate the awareness of Shiraz physiotherapists about ergonomics and its relation with the prevalence of their musculoskeletal disorders. Methods: This cross-sectional study was performed in 2015 on all physiotherapists working in Shiraz hospitals. Data were collected through a questionnaire about the awareness of ergonomics and analyzed through SPSS22 software package. Results: Mean age and work experience of the physiotherapists were respectively 34.06±8.5 and 9.38±7.45 years. Mean awareness of subjects about ergonomics principles, work conditions and the rate of occupational injuries and work problems were respectively 3.15 ± 0.5, 2.70 ± 0.52 and 1.80 ± 0.82 from 5. There was a significant relationship between awareness of ergonomics and musculoskeletal disorders (P=0.04). Increase in awareness of ergonomics was associated with decrease of the risk of musculoskeletal disorders (P=0.04, CI 95% =0.086-0.995, OR=0.259). Conclusion: The results show that increased awareness of ergonomics leads to musculoskeletal disorders reduction. Therefore, compiled educational programs can have a significant impact on learning about right body postures during work and can consequently reduce musculoskeletal disorders and occupational injuries and problems

Car sunshade-induced craniofacial injury: a case report

<p>Abstract</p> <p>Introduction</p> <p>We report the case of a man who sustained a craniofacial injury after spontaneous lateral airbag deployment resulting in his face being struck by a car sunshade. This highlights the potential damage that can be caused by any object placed between a lateral airbag and a car occupant.</p> <p>Case presentation</p> <p>We report the case of a 33-year-old Caucasian man who was the driver in a frontal collision. He had opened the car sunshade and turned it 90° towards the left. As he was driving, he struck a bus, causing the driver's lateral airbag to spontaneously deploy. The airbag pushed the sunshade against his face and injured him.</p> <p>Conclusions</p> <p>Car sunshades can cause significant craniofacial injury. We suggest that sunshade design must be improved to reduce the risk of potential injuries to car occupants. We recommend a new, safer sunshade design.</p

Propagation And Bulb Formation Of Fritillaria (FritillariaImperialis L.) Via In Vitro Culture. Ijpaes.

ABSTRACT: The Fritillariaimperialis is grown natively in Iran. Between ornamental bulblet plants, this plant has special place, therefore this plant needs more attention, otherwise this plant will be destroyed in future. For this reason in vitro culture of Fritillariaimperialis was studied. Tissue culture techniques have high potential for mass propagation. The multiplication efficacy of the method by bulb is low; the plantlets are easy to get diseases and depended on the crop. Plant tissue culture is a technique that has ability of production of a large number of high quality plants. Factors influencing on the regeneration ability and in vitro plantlet growth were examined. The number of regenerated shoots was the highest on MS medium supplemented with 0.5 mg/l TDZ and 30 g/l sucrose; the number of roots was the highest on MS medium supplemented with 0.2 mg/l NAA and 30 g/l sucrose; the in vitro bulb diameter is largest. In vitro plantlets survived in greenhouse at a high rate. A whole process was established for rapid multiplication of Fritillariaimperialis L

Equilibrium current vortices in rare-earth-doped simple metals

Dilute alloys of rare earths have played a vital role in understanding magnetic phenomena. Here, we model the ground state of dilute 4f rare-earth impurities in light metals. When the 4f subshells are open (but not half-filled), the spin-orbit coupling imprints a rotational charge current of conduction electrons around rare-earth atoms. The sign and amplitude of the current oscillate similar to the RKKY spin polarization. We compute the observable effect, namely the Oersted field generated by the current vortices and the Knight shift.Comment: Format: Long articl

Determination of histamine in Iranian cheese using enzyme-linked immunosorbent assay (ELISA) method

Histamine is a simple chemical substance created during processing of the amine acid histidine. Histamine is also an agent in inflammation and the increased presence of histamine causes allergic reaction. Histamine may play a role in the increased prevalence of food intolerances. The objective of this study was to determine histamine contents. Forty four (44) samples of traditional and commercial cheese were analyzed by enzyme-linked immunosorbent assay (ELISA) method in Iran. In the two cheese samples of the 44 samples (4.5%), the presence of histamine was 26 and 46.7 mg/100 g. Histamine in any of the cheese samples was not higher than the tolerance limit of histamine contents (50 mg histamine/100 g) accepted by European countries. The values were comparable and in the range of the literature values. The results of this study indicate that the produced cheese and marketed cheese in Iran have concentrations below 50 mg histamine/100 g. Further studies should be done to investigate the presence of this toxin in different foodstuffs.Keywords: Histamine, cheese, enzyme-linked immunosorbent assay (ELISA), IranAfrican Journal of Biotechnology Vol. 12(3), pp. 308-31