Geometrical simplification of the dipole-dipole interaction formula

Many students meet quite early this dipole-dipole potential energy when they are taught electrostatics or magnetostatics, and it is also a very popular formula, featured in the encyclopedias. We show that by a simple rewriting of the formula it becomes apparent that for example, by reorienting the two dipoles, their attraction can become exactly twice as large. The physical facts are naturally known, but the presented transformation seems to underline the geometrical features in a rather unexpected way. The consequence of the discussed features is the so called magic angle which appears in many applications. The present discussion also contributes to an easier introduction of this feature. We also discuss a possibility for designing educational toys and try to suggest why this formula has not been written down frequently before this work. Similar transformation is possible for the field of a single dipole, there it seems to be observed earlier, but also in this case we could not find any published detailed discussion

First successful autologous chondrocyte implantation in Pakistan

Osteochondritis dissecans entails a hyaline cartilage defect of the articular surface causing pain and functional restriction in young adults, sometimes resulting in early degenerative arthritis. Conventional treatment methods such as abrasion chondroplasty and mosaicplasty have limitations in terms of quality of the resultant cartilage and donor site morbidity. A more recent technique, autologous chondrocyte implantation (ACI) results in hyaline cartilage formation and gives good long-term outcome, but requires a high-level cell culture facility and two surgical procedures. The patient was a young female with knee pain, intermittent locking and feeling of joint mouse . MRI scan and arthroscopy showed a 2 x 2 cm full thickness osteochondral defect in the medial femoral condyle. A free fragment of articular cartilage was found, which was extracted arthroscopically, and chondrocytes were cultured from it in the Juma laboratory. Subsequently, patient underwent surgery whereby the chondrocytes were injected under a periosteal patch sewn over the defect. Over six months, patient\u27s symptoms completely resolved and she returned to full function. A repeat arthroscopy after one year revealed complete filling of the previous defect with normal appearing cartilage indicating success of the procedure. This technology can be utilized for treating patients with a variety of conditions affecting hyaline cartilage of joints

Relationship between Diabetes Type-II and Calcium Ions Concentration in Saliva in Gaza Strip: Retrospective Cohort Study

Saliva contains an amount of calcium concentration; when increased it can play a role in plaque formation on the teeth and can cause the periodontitis disease. Therefore, most diabetic patients show loss of their teeth. In this study, the aim is to investigate the relationship between diabetic disease type-2 and calcium concentration in saliva among diabetic patients in the Gaza strip. A retrospective cohort study will be designed to measure the calcium concentration in the saliva of a random sample of uncontrolled diabetic patients (n=150) and controlled diabetic patients (n=150). The HA1C level in blood will be reviewed in the records of diabetic patients in the diabetic clinic in ten primary health care centers that belonged to the Ministry of Health of Palestinian Authority in Gaza strip governorates in order to follow up and classify conditions of the patients as controlled and uncontrolled. In addition, HA1C in blood and Ca++ level in 2ml saliva will be examined during the conduction of the study for each sample unit (either controlled or uncontrolled patients) in the health laboratory of University of Palestine. The saliva for examination will be collected without any stimulation of salivary gland at 9 a.m. and 12 p.m. after rinsing the mouth with water and allowing 2- 5 minutes for accumulation of saliva. Also, the patient’s periodontal conditions will be evaluated to examine the relationship between diabetes mellitus and periodontitis according to Ca++ level in saliva. The collected data will be by a prepared questionnaire about the socio-demographic, health status, and lifestyle of patients; it will be entered, cleaned and analyzed by using different significant tests at level of significance α=0.05 such as t- test, correlation and regression test by SPSS program

Some Aspects of Arctic Offshore Floating Structures

The present work highlights some aspects related to the analyses of Arctic offshore floating structures. This thesis consists of five papers, which can be divided into two main categories. One category deals with the dynamics of slender structures with an emphasis on the prediction and suppression of vortex induced vibrations (VIV), and the other category examines the process of interaction between sloping structures and sea ice with focus on developing a numerical model to simulate this process in real time. Slender structures, such as mooring lines and marine risers, are very important for the offshore petroleum industry, which is currently approaching deeper waters. Increasingly, attention has been focused on predicting the susceptibility of these structures to VIV. In this thesis, two asymptotic techniques namely, the local analysis and the WKB methods, were used to derive closed-form solutions for the natural frequencies and mode shapes of slender line-like structures. Both the top-tensioned nearly-vertical configuration and the catenary configuration were considered. The accuracy of the solutions derived was established through comparison with other analytic solution techniques and with results of numerical finite element solutions. The effects of the bending stiffness and the effects of approximating the tension variation as a linear function were discussed. Experimental data on the multi-modal in-line and cross-flow response behaviour of a towed catenary model were analysed to examine the usefulness of the solutions for predicting the response frequencies and envelopes due to VIV. Helical strakes are often used as a mitigating measure to suppress the VIV of slender structures. This thesis presented an innovative method to fit ropes helically to a riser in the installation phase. Such a procedure will help to overcome the handling problem associated with the use of conventional sharp-edged strakes. Experimental investigations were then performed to verify the efficiency of these ropes (round-sectioned helical strakes) in suppressing VIV. Systematic experimental investigations including twenty-eight configurations of round-sectioned helical strakes were tested in an attempt to find the most suitable strake configuration. The effects of varying pitch, the surface roughness and the ratio between the cross-flow and in-line natural frequencies on the efficiency of the proposed configuration of round-sectioned helical strakes were also investigated. The process of interaction between sea ice and offshore sloping structures (e.g., conical structures and ship-shaped structures) is quite complex. Modelling this process is very demanding and often computationally expensive, which typically hinders the chances for realtime simulations. This kind of simulation can be very useful for training personnel for Arctic offshore operations and procedures, for analysing the efficiency of various ice management concepts and as a part of the onboard support systems for station keeping. The challenge of meeting the real-time criterion was overcome in the present work. This thesis developed a numerical model to simulate the process of interaction between sea ice and sloping structures in real time. In this model, only level- and broken-ice features were studied. New analytical closed-form solutions were established and used to represent the ice breaking process. PhysX was used for the first time to solve the equations of rigid body motions with six degrees of freedom for all ice floes in the calculation domain. The results of the simulator were validated against experimental data from model-scale and full-scale tests. Accurate predictions of ice actions are also vital to optimise the design of the structures in the Arctic regions. A good understanding of the role of seawater in the process of interaction between the sloping structures and level ice will help to establish reliable models to estimate the ice forces. This work formulated both the static and dynamic bending problems for a floating wedge-shaped ice beam interacting with an offshore sloping structure. For the dynamic interaction, the effects of the water foundation on the bending failure of the ice were studied by comparing the results of an elastohydrodynamic approach with a model of a Winkler foundation. The thesis also investigated the breaking lengths of the ice wedges (i.e., the frequency of the ice loads) as a function of the ice thickness, the compression in the ice and the acceleration of the interaction.PhD i bygg, anlegg og transportPhD in Civil and Transport Engineerin

Report on calibrated and validated numerical models to estimate site specific stability of coastal infrastructure in a changing climate with thawing permafrost

This report presents an overview of the costal erosion model and the infrastructure stability model that are capable of predicting the site-specific response to the global warming and thawing permafrost. The models are developed/modified during the NUNATARYUK project. This report is necessary because the increased Arctic coastal erosion together with permafrost degradation pose a significant threat to the communities living close to the coasts. It provides a brief description of the models, and their calibration procedures, and demonstrates a couple of validation case studies. The costal erosion model described in this report is a comprehensive process-based model. It couples the thermodenudation and thermoabrasion processes with nearshore hydrodynamics and sediment transport. A couple of open-source packages are combined in this model with in-house models/codes to simulate the Arctic coastal erosion processes in a sequentially coupled manner. A simplified 1D storm surge module introduced by Dean and Dalrymple (1991), and the SWAN package developed at TU-Delft (TU-Delft, 2021) are employed to simulate the storm surge and wave generation in the offshore zone, respectively. The waves and related hydrodynamic forces together with sediment transport and morpho-dynamics are simulated using XBeach (Deltares, 2022). The processes related to permafrost melting and erosion of the bluffs are simulated with in-house modules implemented in XBeach. The model is calibrated and validated with field measurements from one of the Arctic coasts along the Kara Sea. The simulations confirms that the erosion mechanism is greatly influenced by the nearshore hydrodynamics and provide justification for including a hydrodynamic model to simulate Arctic coastal erosion. The coastal infrastructure stability model in this report is a thermo-hydro-mechanical (THM) constitutive model that can represent the behaviour of frozen and unfrozen soil at the representative elementary volume (REV) scale, and in a unified manner. The presented model can describe the mechanical behaviour of frozen soil, including creep, as function of temperature, up to the unfrozen sate and vice versa. The model is designed for clay material, but the idea behind the model can be extended for sand as well. The model is implemented in Plaxis package, which is a software widely used by geotechnical engineers, and is capable of simulating the coupled THM behaviour of porous media, like clay deposits, at the global scale, using the finite element (FE) method. The calibration procedure is described in the report. All model parameters can be found using laboratory tests at the REV scale. The model is calibrated and validated using the field measurements conducted in the National Geo-test Site located at Longyearbyen Svalbard, and reasonable agreements have been achieved. It is also used to simulate the permafrost degradation and settlement of a footing with various embedment depth and applied stress for different imposed warming scenarios for the next 50 years. The simulations results confirm the importance of creep deformation for the serviceability and stability of infrastructures on warming permafrost, particularly in clay deposits.publishedVersio

Comparison of the Dichlorination of Organic N-Chloramines by Caroate and by Bisulfite: A Kinetic Study

Bisulfite is commonly used to dechlorinate chlorinated municipal wastewater. However, several studies suggest that bisulfite is not effective in dechlorinating N-chlorinated amino components of wastewater. The purpose of this study was to investigate the effectiveness of an alternate dechlorinating agent, caroate (peroxysulfate), and to compare its rate of dechlorination of three different types of chloramines with that of bisulfite. Four N-chlorinated amino compounds were investigated: N-chlorodiethylamine, N­ chloroalanylphenylalanine, N-chloroglycylphenylalanine, and N-[2-(N\u27-chloroimino)­ propanoyl]phenylalanine. These compounds were selected from different families of N­ chloramines to study the effect of structure on dechlorination by both caroate and bisulfite. At pH 7.0 and at 23 °C, caroate dechlorinated N-chlorodiethylamine, N-chloro­ alanylphenylalanine, N-chloroglycylphenylalanine, and N-[2-(N\u27-chloroimino)propanoyl]­ phenylalanine with the calculated second order rate constants of 27.7 (±0.96) M-1min-1, 2.61 (±0.01) M-1, 1.31(±0.09) M-1min-1, and 7.1 (±0.25) x 10-2M-1 min-1 respectively. Under the same conditions, the second order rate constants for the dechlorination of the same compounds by compounds by bisulfite were found to be 1.63 (±0.14) x I0\u27M-1 min-1, 1.86 (±0.09) x 103 M-1 min-1, 2.12 (±0.13) x 103 M-1min-1,7.8 (±1.5) x 1D2 M-1min-1, respectively using HPLC. When using amperometric titration at the same pH and temperature, the second order rate constants for these compounds were found to be 1.29 (±0.17) x 105 M·1 min·\u27, 2.37 (±0.19) x 103 M· 1min•1, 2.01 (±0.11) x 103 M 1min·1, and 8.5 (±0.07) x 102 M·\u27 min·\u27, respectively. In conclusion, caroate was found to be a very slow dechlorinating agent compared to bisulfite and it is not fast enough to replace bisulfite in the dechlorination of wastewater in treatment plants. Furthermore, the N-chloroketimines compared to the simple N-chloramines and N-chlorodipeptides studied was slowly dechlorinated by bisulfite. As a result it is likely that N-chloroketimines contribute to the pool of total residual chlorine compounds which are poorly reduced in the dechlorination of wastewater effluents by bisulfite