Search

The coronavirus (COVID-19) has challenged healthiness careers and techniques and has induced several rates of reaction and forms of reaction worldwide. The responsibility of dental specialists in inhibiting the transmission of COVID-19 is seriously significant. Dental professionals suffered a proper duty to decrease routine care for fear of increasing COVID-19 among their patients and elsewhere but were understandably concerned about the economic concerns. This paper explores comments raised by orthodontists worldwide about offering safe orthodontic service during the ongoing COVID-19 pandemic, as orthodontic treatment procedures increase the possibility of transmission. As proximity between the orthodontist, dental assistant, and patient is required for treatment, it jeopardizes the health of all the parties involved. In this paper, we will highlight five issues: general principles, communication, dental clinic admission, infection control measures, and applied orthodontic treatment emergency. Upon reviewing these issues, we will then attempt to formulate appropriate orthodontic treatment guidelines applicable in this specific era.

Vaginal discharge in women is occasionally caused by aerobic bacterial organisms. The study aimed to determine the etiology of female vaginosis and their antibiotic sensitivity pattern. HV culture results, age, and sex of all female patients with suspected bacterial vaginosis were collected. High vaginal swabs were inoculated into MacConkey agar, 5% blood agar, and chocolate agar and then incubated at 37°C in the presence of 5% CO2 for 24-48 h. The antimicrobial susceptibility testing was performed by the disk diffusion method. Ten different antibiotic discs were used: Amikacin, Augmentin, Ceftazidime, Ceftriaxone, Ciprofloxacin, Gentamicin, Levofloxacin, Meropenem, Septrin, and Clindamycin. After 24 hours, zones were measured in mm, and zone interpretations were in accordance with the National Committee for Clinical Laboratory Standards criteria guidelines. A total of 215 females were included in the study, the incidence of bacterial vaginosis was 18.6% (40/215). Females between 33 and 45 years old had a somewhat high prevalence (19/40:47.5%) of bacterial vaginosis. The most frequent isolates were 45% (18/40) Escherichia coli followed by 15% (6/40) Strep pneumonia. The in vitro susceptibility tests of the most common isolates showed high resistance levels to commonly used antibiotics such as Augmentin and Gentamycin. Whereas highly sensitive rates were observed for Ceftriaxone 70%, followed by Ciprofloxacin 57.5%. Ceftriaxone and Ciprofloxacin showed the best antibiotic sensitivity. Additional studies are necessary to recognize those bacterial species that cause vaginal infections and determine the susceptibility of those species to recently used antibiotics.

Colorectal cancer is the third common cancer, and the second common cause of cancer death in the world. According to the 2014 Cancer Incidence Report of the Kingdom of Saudi Arabia, colorectal cancer account for 11.5% from all cancers reported among Saudi nationals. By the year 2030, the incidence of colorectal cancer could increase fourfold among both genders.The study aimed to conduct to understand the knowledge, attitude, and practice of primary healthcare physicians regarding colorectal cancer screening in Riyadh Second Health Cluster in the city of Riyadh, Saudi Arabia.A cross-sectional study design, probability proportional to size sampling at the cluster zones level and convenient sampling for the physicians, were used among physicians working in the primary healthcare centers in the city of Riyadh between October 2022 and November 2022.Of the 213 respondents, the mean age of the physician was 35, the majority were males (59%), Saudi Arabian nationality (60%), Resident Physicians (54%) and ≤ five years' work experience (45%). Sixty-four percent of the study participants believe that the majority of asymptomatic average-risk patients have to start the screening at the age of 45 years old. Ninety-seven percent believe that colorectal cancer screening for asymptomatic average-risk patients aged 45 years and older is effective. Ninety-two percent of the physicians perform colorectal cancer screening for asymptomatic average-risk patients aged 45 years. The mean knowledge score is 4.65 (SD=2.33) with a range of 0 to 10. The mean attitude score is 4.19 (SD=1.28) with a range of 0 to 6.The study found that the physicians had higher attitude and practice towards colorectal cancer screening and adequate knowledge towards colorectal cancer screening. The knowledge and attitude scores are associated with practicing colorectal cancer screening.

The advent of laparoscopic techniques in repairing inguinal hernia has significantly improved outcomes of inguinal hernia surgery. However, acute and chronic postoperative pain after fixation of mesh with tacks and the cost of tacking devices are major hindrances to the widespread use of laparoscopic transabdominal preperitoneal (TAPP) repair in resource-poor settings. This study sought to introduce a method of mesh fixation that will reduce the cost of laparoscopic TAPP repair and might help reduce postoperative pain.To compare outcomes in the early postoperative period like pain, seroma, hematoma, urinary retention, and neuralgia after fixation with suture versus the tack fixation of mesh in laparoscopic TAPP repair of inguinal hernia. Subjects and methods: This study was conducted from 1 The age range was 18 to 60 years with a mean age of 46.53 years ±10.01 S.D in Group A and 46.19 ±9.58 S.D in Group B. In Group A 98.6% of patients were male, and 1.4% were females while in Group B 100% of patients were male. It was found that mean pain in Group A was 4.88 ±0.887 and 5.29± 0.777 at 6 hours and 24 hours respectively. Mean pain in group B was 3.43 ±0.962 and 4.11±0.703 at 6 hours and 24 hours respectively. Moreover, mean pain in Group B was significantly less than mean pain in Group A both at 6 hours and 24 hours intervals with a p-value0.001. The early postoperative complications were not significantly different in both groups. Conclusion: In TAPP repair, suture fixation of mesh is less painful than tack fixation. However, there is no significant difference in the rate of other early postoperative outcomes like seroma, hematoma, urinary retention, and neuralgia. Further multicentric studies with a longer duration of follow-up are needed to validate our results.

Cutting forces play a significant role in machining because they directly affect the mechanics of machining, the energy requirements, and the tool stability required. In this study, the cutting forces occurring during the turning of AISI 4340 material with 30 Rockwell C hardness scale have been analyzed both experimentally and numerically. Many types of research have been conducted via 2-D simulation using the finite element analysis method. In other words, in most studies, the workpiece was modeled as a flat specimen. Therefore, this paper presents a real 3-D turning simulation model using cylindrical specimens. The cutting forces were measured using a Kistler 9129AA model piezoelectric dynamometer. The ABAQUS/Explicit finite element method was used, and a model by Johnson and Cook was assigned as a material model in the numerical analysis. A new PVD AlTiN coated carbide insert was incorporated to prevent wear. Experimental results obtained from cutting tests were compared with numerical results to establish the accuracy of the FEM. It was observed that experimental and numerical results overlapped each other. Thus, this method can be used directly in the industry to reduce high processing costs.

In this study, effects of cutting speed (V), feed rate (f), depth of cut (a) and tool tip radius (R) on surface roughness (Ra, Rz, and Rt) and cutting forces (radial force (Fx), tangential force (Fy), and feed force (Fz)) in hard finish turning processes of hardened 42CrMo4 (52 HRC) material was investigated experimentally. Taguchi’s mixed level parameter design (L18) is used for the experimental design (2x1,3x3). The signal-to-noise ratio (S/N) was used in the evaluation of test results. By using Taguchi method, cutting parameters giving optimum surface roughness and cutting forces were determined. Regression analyses are applied to predict surface roughness and cutting forces. Analysis of variance (ANOVA) is used to determine the effects of the machining parameters on surface roughness and cutting forces. According to ANOVA analysis, the most important cutting parameters were found to be feed rate for surface roughness and depth of cut among cutting forces. By conducting validation experiments, optimization was seen to be applied successfully.

Given the increments of a simple symmetric random walk $(X_n)_{n\ge0}$, we characterize all possible ways of recycling these increments into a simple symmetric random walk $(Y_n)_{n\ge0}$ adapted to the filtration of $(X_n)_{n\ge0}$. We study the long term behavior of a suitably normalized two-dimensional process $((X_n,Y_n))_{n\ge0}$. In particular, we provide necessary and sufficient conditions for the process to converge to a two-dimensional Brownian motion (possibly degenerate). We also discuss cases in which the limit is not Gaussian. Finally, we provide a simple necessary and sufficient condition for the ergodicity of the recycling transformation, thus generalizing results from Dubins and Smorodinsky (1992) and Fujita (2008), and solving the discrete version of the open problem of the ergodicity of the general L\'evy transformation (see Mansuy and Yor, 2006)., Comment: 22 pages, 2 figures

Introduction/Background* The presentstudywascarried out over a 1-year period (January 2017-December 2017) and conductedat the cytology unit of PathologyDepartment (Salah Azaiez Institute, Tunisia). It included all patients withbreastlesionreferred to our unit. Smearswerefixed and stained by May GrunwaldGiemsa .Cytologyresultswerecategorizedaccording to the NCI by twocytopathologistsindependently. Methodology The presentstudywascarried out over a 1-year period (January 2017-December 2017) and conductedat the cytology unit of PathologyDepartment (Salah Azaiez Institute, Tunisia). It included all patients withbreastlesionreferred to our unit. Smearswerefixed and stained by May GrunwaldGiemsa .Cytologyresultswerecategorizedaccording to the NCI by twocytopathologistsindependently. Result(s)* FNAC interpretivecategorizationwas as follows : 188 (31,3%)inadequate (C1), 378 (63%) benign (C2), 1 (0,16%) atypical, probablybenign (C3), 31 (5,14%) suspicious of malignancy (C4) and 2 (0,4%) malignant (C5).The histopathologicalexamination of category C3 showed a benignlesion.Histopathologicalexamination of category C4 wasassessedonly for 20 patients. 14/20 cases showedbenignlesions, in one case an in-situ carcinomawasdiagnosed and 5/20 cases showedmalignancy.The positive predictive value of C4 category in the diagnosis of malignancywas 30%. Conclusion* FNA is a safe and cost-effective technique for the diagnosis of breastlesions, especiallywhencorrelatedwithclinical and imagingstudies. It has achievedgreat importance in diagnosis and management of palpable breastlesions. However, we must beaware of possibility of “false positive” and “false negative” resultsespecially for categories C3 and C4.

Introduction/Background* Triple-negative breast cancer(TNBC) represent a consistent subgroup of breast cancers with heterogeneous clinical presentation, clinical behavior, histology, and response to therapy. Awareness of TNBC was recently increased by the discovery of the intrinsic molecular subtypes in breast cancers with gene expression profiling experiments. At least five molecular categories have been repeatedly identified in breast cancer, each with prognostic significance. Methodology We retrospectively reported 18 cases of tripe negative cancer treated at salah azaiez institute Tunisia between 2016 and 2021.including 3 cases of CAK (adenoid cystic carcinoma), 10cases of CI-TNS-CM (medullary carcinoma) et 5 cases de CA (apocrine carcinoma). Result(s)* The average age was 68 years. The mean tumor size was 37mm. In 15/18 cases the tumors were grade III SBR modified. Lymphatic emboli were observed in 4 cases/18. The Ki67 was on average 57%. Metastatic lymph nodes were identified in 4 cases out of 14 having had axillary dissection. Conclusion* The prognostic value of classical pathological variables such as tumor grade, lymph node status, and tumor size, could be impaired in TNBC. Indeed, most TNBC are high grade, and first generation prognostic molecular assays, which are driven mainly by proliferation, did not show prognostic value in TNBC. In contrast, Ki67 stainings in TNBC have been suggested to carry prognostic information in some reports but not in others.8Small (cT1a/b) node-negative TNBC are potentially aggressive as well. Despite the abovementioned issues, the Nottingham Prognostic Index (NPI) has been reported to be useful in TNBC.

Introduction/Background* The incidence of breast carcinoma cutaneous manifestation in patients with breast carcinoma is 23.9%. The most common sites of breast carcinoma cutaneous manifestation are the chest wall and abdomen, but they can occur at the extremities and in the head/neck region. Due the high incidence of breast carcinoma, these cutaneous manifestations are the most common metastases seen by dermatologists. Methodology We retrospectively reported 20 cases of cutaneous metastasis from breast carcinoma diagnosed at salah azaiez institute Tunisia between 2015 and 2021. Result(s)* there were a total of 20 cases of cutaneous metastasis from breast cancer. The average time interval between diagnosis of breast cancer and cutaneous presentation was 4years.The cutaneous sites of involvement included the head and neck (5) , the trunk (10), the extremities (3), and multiple sites (2). The age range was 38–83 Conclusion* Skin metastasis from breast cancer is frequent . The diagnosis is easy by biopsy or surgical excision.The molecular profile is variable according to the behavior and the aggressiveness of the primary tumor, an in-depth histological study is necessary to dictate the management.

In this study, cutting forces and chip shapes formed by turning cylindrical materials were researched experimentally and numerically. AISI 4340 steel alloy with a hardness of about 30 Rockwell C scale was chosen as workpiece material. Most of the turning simulations performed by finite element method (FEM) have been conducted 2D (two-dimensional) because 3D (three-dimensional) is very difficult and time-consuming and mechanics of more complex 3D cutting operations are usually evaluated by using geometrical and kinematic transformation models applied to the 2D cutting Process. In other words, the workpiece was modeled as a flat specimen. Nevertheless, 3D (three-dimensional) simulation using cylindrical models are more nearer to practical process. For this reason, to get the actual cutting process, this paper aims to present a real 3D (three-dimensional) turning simulation model using ABAQUS/ Explicit software using tube and bar specimens with a cylindrical shape. Cutting forces were measured utilizing the Kistler 9129AA model piezoelectric dynamometer. Cutting forces and chip shapes obtained by making FEM simulations were compared. Simulation results were determined to be in high proximity with experimental results. Also, realistic chip shapes were simulated by FEM. Therefore, this method could be used as reliable in the industry.

Significance In a popular parlor trick, plasma is created by irradiating grape hemispheres in a household microwave oven. This work ties the source of the plasma to microwave photonic hotspots at the junction of aqueous dielectric spherical dimers. We use a combination of thermal-imaging techniques and computer simulations to show that grape-sized fruit and hydrogel beads form resonant cavities that concentrate electromagnetic fields to extreme subwavelength regions. This is enabled by the large dielectric susceptibility of water at microwave frequencies. Furthermore, the absorptive properties of water are key to washing out complex internal modes and for allowing the evanescent hotspot build-up. Our approach to microwave resonances in high-dielectric materials opens a sandbox for nanocluster photonics research., The sparking of cut grape hemispheres in a household microwave oven has been a poorly explained Internet parlor trick for over two decades. By expanding this phenomenon to whole spherical dimers of various grape-sized fruit and hydrogel water beads, we demonstrate that the formation of plasma is due to electromagnetic hotspots arising from the cooperative interaction of Mie resonances in the individual spheres. The large dielectric constant of water at the relevant gigahertz frequencies can be used to form systems that mimic surface plasmon resonances that are typically reserved for nanoscale metallic objects. The absorptive properties of water furthermore act to homogenize higher-mode profiles and to preferentially select evanescent field concentrations such as the axial hotspot. Thus, beyond providing an explanation for a popular-science phenomenon, we outline a method to experimentally model subwavelength field patterns using thermal imaging in macroscopic dielectric systems.

When grape-sized aqueous dimers are irradiated in a microwave oven, an intense electromagnetic hotspot forms at their point of contact, often igniting a plasma. Here we show that this irradiation can result in the injection of mechanical energy. By examining irradiated hydrogel dimers through high-speed imaging, we find that they repeatedly bounce off of each other while irradiated. We determine that an average of 1 μJ of mechanical energy is injected into the pair during each collision. Furthermore, a characteristic high-pitched audio signal is found to accompany each collision. We show that both the audio signal and the energy injection arise via an interplay between vaporization and elastic deformations in the region of contact, the so-called 'elastic Liedenfrost effect'. Our results establish a novel, non-contact method of injecting mechanical energy into soft matter systems, suggesting application in fields such as soft robotics.

The design and analysis of GaN HEMT linear power amplifier to operate at 6 GHz frequency is presented in this work. The GaN HEMT with 800 nm gate length, was power matched at the frequency of 6 GHz. The linear model of the GaN HEMT was derived from the scattering parameter data for designing the power amplifier. The power amplifier displayed a power gain of 9 dB and noise figure of 2 dB at 6 GHz frequency. The Rollet’s Stability factor of the linear power amplifier at 6 GHz frequency is 1.4, hence the amplifier is stable. The scattering parameters of the GaN HEMT power amplifier were also obtained. At 6 GHz frequency the power amplifier exhibited an input return loss of -19 dB.

The DC and high frequency performance of AlGaN/GaN HEMT device with and without the AlGaN back barrier was studied and the performance of the devices are compared. Introducing the back barrier helps in lifting up the conduction band and thus minimizes the leakage path under the buffer layer and also helps in confining the 2DEG in the narrow channel. Also with the introduction of the back barrier, the drain leakage current in the subthreshold region is significantly minimized and the DC charecteristics of AlGaN/GaN HEMT is preserved. At the same time the RF performance is enhanced by reducing the short channel effects.

Spatial distribution functions have become an important tool in the analysis of organic molecules in aqueous systems. Here we establish a technique of differential spatial distribution functions to help analyze hydration of organic compounds with aromatic rings. We find that the π bonding of hydrated molecules is most sensitive to any changes in molecular structure and temperature. We also test different interaction potentials currently available for aromatic molecules, and find that aside from small differences in π bonding, there is generally no significant effect on coordination structure.

This paper presents the performance of a single effect absorption cooling system under three different climates in Saudi Arabia. The considered system capacity is 10.5[Formula: see text]kW and uses LiBr/water pair. The study results indicated that considering the dynamic response of the cooling cycle significantly increases (close to 30%) the time taken to reach steady-state operations and that the sensitivity of the system to form precipitation of LiBr also increases. Also, the dynamic performance was investigated under different heat inputs and resulted in shorter transient period with increasing the heat input. In addition, the performance of the solar absorption system was investigated for a representative summer day in different climatic regions in Saudi Arabia. The results indicated the requirement of different areas of collectors to meet the absorber heating demand from 09:00 a.m. to 04:00 p.m. if there is no auxiliary heating. Auxiliary heating is required from 04:00 p.m. to 09:00 a.m. Finally, the results indicated that the system performs better in Riyadh city than in Dhahran and Jeddah. This study emphasizes the importance of taking into consideration the thermal inertia of the system components when analyzing the performance of such systems.

This paper presents development of a dynamic model of a 3 TR single-effect absorption cooling cycle that employs LiBr-water as an absorbent/refrigerant pair coupled with solar collectors. Due to the frequently changeable cooling load, and the freckle nature of the solar radiation which indirectly provides the heat input; the system performance is highly transient. Even if, the input power from the solar field is controlled, there will be an unsteady period that precede the steady operation period of the cooling system. Throughout this transient period, most parameters keep fluctuating and do not stabilize at particular values, and some of them may go away from their allowed ranges in a manner that affects the system performance severely. This phenomena is considered as a prime motivation and fundamental concern of this study. The dynamic model is based on mass, energy balances and heat transfer equations while taking into account the dynamic response of the cycle. The results indicate that it takes an average of fourteen minutes before most parameters stabilize at their operating values and the dynamic terms almost diminish in what could be considered steady-state period. In addition, the performance of a solar absorption system was investigated under meteorological conditions of Dhahran — Saudi Arabia for a representative summer day. The results indicated that; a 60 m2 of evacuated tube solar collectors is needed to meet the 3 TR cooling load without auxiliary heating during the period 8:00 a.m. to 3:00 p.m. an auxiliary heating is required outside this period to meet the cooling load. The developed dynamic model is able to predict the transient performance of a 3 TR single-effect LiBr-Water solar absorption cooling system which in turn helps in designing appropriate integrated systems for various sustainable applications.

The sparking of grapes in a household microwave oven is a popular yet largely unexplained phenomenon. Using FDTD simulations, high-speed videography, and thermal imaging, we tie this phenomenon to low-Q Mie resonances in aqueous dimers.

In this study, the effect of shot peening parameters on fatigue strength of steel manufactured by powder metallurgy (PM) was investigated. Steel material obtained from Hoganas ASC 100.29 in chemical composition of Fe–0.5% C–2% Cu was produced by using a single action press PM process. To determine the effect of shot peening parameters on fatigue performance, fatigue tests were performed on 20 unpeened and 80 shot-peened samples, which were machined from sintered steel. Furthermore, shot-peened samples were peened at different peening intensities, 100% and 200% saturation and full coverage conditions. Fatigue performance of steel, produced by PM process, was improved by surface peening process. For the studied PM steel, the best fatigue performance was obtained with the samples that were shot peened at 20 Almen intensity and 100% saturation. Fatigue strength and limit of the samples, however, were reduced after a certain cold work level. Higher intensity and saturation levels of peening process thus deteriorated the beneficial effect on fatigue strength and limit.

The internet of things technologies can be exploited to provide the museum visitors with many kinds of advanced services. The visitor interests are renovated and the smart environment within a museum provides an interactive experience for the visitor. In this work, we design a wearable museum guide which can automatically provide the audio description of the museum collection the visitor is observing. Along with the image recognition capability, the wearable device also has localization feature. The museum admin is able to continuously track the user within the museum. This is achieved using a Bluetooth Low Energy infrastructure installed within the museum. The localization information can be used to provide more services for the visitors and also used by the museum staff for museum maintenances. All the cultural contents are stored in the cloud and retrieved whenever they are demanded by the user. The item is identified and the corresponding description is fetched from the cloud and automatically played as an audio or video. This system has helped the museum visitors to explore freely and make the museum visit a personalized one.

The conservation of migratory wildlife species in the savannah habitat can be a challenge because of frequent and prolonged drought and their requirements for a large area. We investigated the performance of the wildebeest (Connochaetes taurinus) population in the 25,624 km2 Kilimanjaro landscape of Kenya and Tanzania, which comprises Amboseli-West Kilimanjaro-Magadi-Natron after 2009 drought. We used total aerial counts to determine the spatial distribution and numbers of wildebeests during wet and dry season in 2010 and 2013. Global Positioning System and digital voice recorders were used to count wildebeests along established transects within blocks. There was an increase in the wildebeest population by 103% during the wet season and 14% during the dry season between 2010 and 2013. The seasonal variation in density occurred between the four counting blocks with Natron and Magadi areas recording the highest densities. Generally, the increase in population could be attributed to the recovery of the population after the 2009 drought. The current cross border collaboration between Kenya and Tanzania in aerial surveys is an important step in the conservation of this migratory species in the landscape. This study demonstrates that detailed knowledge of density and spatial distribution of migratory species is required to plan effective conservation action.

External thread cutting is a complex 3-D process in which the cutting conditions vary over the thread cutter profile. It is accepted as a mature technology. However, thread machining is heavily experience-based technology and there are few academic works published. Determining the cutting forces during machining is crucial to explain formation of the surface layer, residual stresses, selection of the most appropriate machine tool, and optimizing the process. Mechanistic force model is known to be the most developed method in machining processes. In orthogonal cutting, the material is removed by the cutting edge that is perpendicular to the direction of relative tool-work motion (direction of the cutting velocity). Although the most cutting operations are three-dimensional, orthogonal cutting is used to explain the general mechanics of the material removal. In this study, tangential and radial cutting forces during thread cutting which has API-V0.040 thread profile were predicted from the orthogonal cutting data of the AISI 4140 steel. Huge differences up to 60 % were observed between predicted and measured cutting forces. Therefore, mechanistic force model was improved for thread cutting operations and cutting forces were predicted with average errors between 3 and 18 % depending on machining parameters.

External thread cutting is a complex 3-D process in which the cutting conditions vary over the thread cutter profile. It is accepted as a mature; however, heavily experience based technology and there are few academic work published. Determining the cutting forces during machining is crucial to explain formation of the surface layer, residual stresses, selection of the most appropriate machine tool and optimizing the process. This investigation is an attempt to predict thread cutting forces by dividing the thread chip into three parts, one thread root and two side faces. Variation of the cutting parameters including the shear angle, mean cutting temperature and friction force on the flank face of the tool along the thread tool root and sides are determined. In the thread root and sides, chip compression ratios for the V-shaped single piece and separately cut chip zones are measured and cutting forces are calculated and compared for precision metric thread cutting on a SAE 4340 steel bar.

A portable solar water heater was designed, built and tested. This application of solar energy devices is particularly important for the Bedouin community which can gain a great deal from the solar energy that is continuously available in the desert. It can be also used by campers and those who use recreation vehicles. A normal satellite dish of 150 cm diameter was used as a concentrator for solar radiation. The surface of the dish was covered with reflective aluminum foil which was used to concentrate solar energy on a cooking pot in one mode of operation. This mode was operated in two ways: one with bare pot and the other with the pot being covered with glazing by putting it inside a glass box. The device was also used in another mode of operation to heat water for domestic use by placing a specially designed solar collector in the focus. It was found that, when the device was operated in the bare cooker mode, a 7 kg of water at 20 °C was brought to a boil in 1 h. Putting the pot inside the glass box reduced the time required for boiling to 40 min and the cooking power was increased by 275%. In the collector mode, the device was able to heat 30 kg of water from 20 °C to 50 °C in 2½ h. The highest efficiency obtained for this mode was 77% and the slope of the efficiency curve was −10.63 W/m 2 °C.

The strain hardening and the formation of the residual stresses at the roots of threaded joints produced by machining according to American Petroleum Institute (API) standards was investigated. Initially the problem is defined and then an experimental technique was developed for measuring the residual stresses at the roots of fine screw threads. The screw thread was cut on a tubular bar from chromium–nickel based alloyed steel. Residual stresses were measured by the electro-chemical layer removal technique. Experimental work showed that, sever strain hardening and the concentration of residual stresses at the roots of the screw threads took place depending on the machining conditions. Strain hardening in the range of 320–430 HV were found on the screw thread surfaces as compared to the base hardness of 260 HV. Residual stress ranging from 600 to 1450 MPa was developed as compared to the material tensile strength of 850 MPa. The depth for maximum residual stress is around 20 μm.

The effects of machining parameters on the fatigue strength of fine-machined threaded specimens were investigated by comparing with the endurance limits of circumferentially notched specimens with the same profile. A four-point rotary bending fatigue test machine was used to obtain constant bending moment and pure alternating stress along the thread. All specimens were machined from SAE 4340 steel, the typical material used for deep well oil drilling pipes. Notched specimens were fine-machined according to ASTM standards, while the threaded specimens were machined under the optimized cutting conditions, which maximize tool life and geometric precision, as well as under selected modified conditions. Endurance limits of all specimens after 2 × 10 6 cycles were experimentally determined and S – N curves were plotted for 90% reliability for all experiments. The effects of cutting force, radial feed, tool wear, and two thread cutting methods on the fatigue strengths of the threaded specimens were determined. Experimental results show that the fatigue strengths of threaded specimens lie within a large range, depending on machining conditions, as compared to circumferentially notched specimens. The most influential factors on the fatigue strength of threaded specimens are tool wear and cutting velocity, while the effects of cutting method and radial feed are less significant.

Design and machining of the fatigue test specimens have significant effects on the duration and reliability of fatigue test. Fatigue test specimens essentially consist of three parts: the center or critical test section, which is the region where required conditions are simulated as closely as possible, and the two ends, which serve to transfer the load from the grips to the center section. When high strength materials are used for a complex geometry, such as a thread need to be tested, design and manufacturing of the specimens become more influential on the reliability and duration of the tests. Threaded fatigue test specimens were designed, machined, and tested in a four-point rotary bending fatigue testing machine. An innovative threaded fatigue test specimen that consistently fails at the critical test section was designed, machined, and tested successfully to give the required fatigue notch factor. Because of full scale fatigue testing with threaded parts is very expensive and sometimes dangerous, evaluated threaded fatigue specimen can be used in fatigue testing and it reduces duration of the experiment more than 60% for machined threaded specimens.

We prove that if the Black-Scholes formula holds with the spot volatility for call options with all strikes, then the volatility parameter is constant. The proof relies some result on semimartingales (Theorem 2) of independent interest.