Nonlinear Vibrations of 3D Laminated Composite Beams

A model for 3D laminated composite beams, that is, beams that can vibrate in space and experience longitudinal and torsional deformations, is derived. The model is based on Timoshenko’s theory for bending and assumes that, under torsion, the cross section rotates as a rigid body but can deform longitudinally due to warping. The warping function, which is essential for correct torsional deformations, is computed preliminarily by the finite element method. Geometrical nonlinearity is taken into account by considering Green’s strain tensor. The equation of motion is derived by the principle of virtual work and discretized by the p-version finite element method. The laminates are assumed to be of orthotropic materials. The influence of the angle of orientation of the laminates on the natural frequencies and on the nonlinear modes of vibration is presented. It is shown that, due to asymmetric laminates, there exist bending-longitudinal and bending-torsional coupling in linear analysis. Dynamic responses in time domain are presented and couplings between transverse displacements and torsion are investigated

Dynamics of macrozoobenthos in the Southern Bulgarian Black Sea coastal and open-sea areas

The paper presents results of analysis of 96 macrozoobenthic samples, collected on a seasonal basis in Bourgas Bay and in open-sea areas offshore Cape Emine (Bulgarian Black Sea) in 1996 and 1998. In total 96 taxa were established, distributed in four groups: Polychaeta, Mollusca, Crustacea and “Diversa”. The average density of populations was 1756 ind.m-2 with a predominating abundance of Polychaeta species. The average biomass estimated was 183.02 g.m-2, formed mainly by representatives of Mollusca. The latter species were measured together with the shells, which appraised their individual weights. Seven of the species found had a coefficient of constancy more than 50%. These were the most adapted species to the environmental conditions of the investigated areas. The quantitative and qualitative assessments in this study demonstrate an increasing tendency in the parameters obtained (density, biomass, species diversity) in comparison with previous investigations in the early 1990-s, when intensive anthropogenic influence was widely perceived to misbalance the Black Sea ecosystem.The method of Warwick (1986) applied to characterize the water quality of the studied areas allowed us to define them as rather clean or moderately polluted aquatories

Biocompatibility of materials and products used in medicine and dental medicine

BackgroundBiomaterials are defined as substances intended to replace a part of the body or its function in a secure, safe and economical way, while being physiologically and aesthetically acceptable. Biomaterials can be bioinert or regenerative. Biocompatibility refers to the ability of a material to elicit a specific biological response after administration in a living organism. Measuring the biocompatibility of materials used in dentistry is not an easily achievable task.MethodsScientific databases – PubMed, Scopus and Medline, as well as monographs, textbooks on the topic, websites were used to search for the data required. The following keywords were used: biomaterials, biocompatibility, dental medicine, medicine, toxicity.The aim of the following article is to summarize the main conclusions authors in the field have reached to when discussing biocompatibility and tolerance of material and products used in medicine and dental medicine.Results and discussionIn depth results and discussion are presented in the section. Materials used in medicine and dental medicine encompass a wide range of compounds, with different chemical and physical structures. Therefore, profound knowledge is needed to be able to treat the patients and keep them safe as much as possible from possible adverse biological reactions.ConclusionsMedical and dental specialists should pay special attention to the content of the materials they implement in their treatment plans on a daily basis. Being profoundly informed on the general diseases, medications usage and allergic status of their patients can prevent adverse complications. Although medicine explores and studies in depth possible biological reactions, still they may occur

Prediction of sanding in subsurface hydrocarbon reservoirs.

Sand production in oil and gas wells can occur if the fluid velocity exceeds a certain value. Due to drilling operations, the mechanical stresses can exceed the load bearing capacity of the rock. As the local stresses exceed certain level, a certain amount of rock is fractured into sand. Then, the sand is carried by the fluid through the wellbore depending on the flow rate. The amount of the solids can be less than a few grams per cubic meter of reservoir fluid or an essential amount. In the later case erosion of the rock and removing sufficient quantities of rock can occur. This can produce subsurface cavities which collapse and destroy the well. When sanding is unavoidable it is necessary to estimate the characteristics of the process. Our aim was to generate a simple one-dimensional local model, which predicts the volume of sanding, the radius and the porosity of the yielded zone. Such model will help the company in the development of complex 3D models

History of the World Hearing Day

BackgroundAccording to recent data from the World Health Organization from 2019, approximately 466 million people are living with a disabling hearing loss, most of them in low- and middle-income countries. Undiagnosed and untreated hearing disorders are proven to be a leading cause for morbidity and cost annually $750 billion. Hearing disorders and hearing loss are believed to higher their prevalence due to the fact that a wide majority of people are exposed to high noises and lack of timely and adequate hearing diagnostics and treatment of ear conditions.MethodsScientific databases – PubMed, SCOPUS and MEDLINE were used to search for the information targeted. The following keywords – World Hearing Day, history, events, prophylaxis, hearing disorders were used. Information from the official websites of the societies involved in celebrating World Hearing Day was included as well. The aim of the following article is to study the history of the event from its foundation till today, aiming to stress out its usefulness. Results and discussionBack in 1995, World Health Assembly passed a resolution WHA48.9, in which attention of the health impact of hearing loss was put – 120 million people worldwide were living with a disabling hearing difficulties. During the World Health Assembly in 2017, with the adoption of the resolution WHA70.13, hearing care and hearing loss were highlighted as a public health issue. Authors claim that most of the causes for hearing loss are preventable.World Hearing Day is an international campaign, organized annually by the Office of Prevention of Blindness and Deafness of the World Health Organization (WHO) on March, 3rd. Organizers claim that World Hearing Day is the largest global awareness event, aiming to bring society’s attention to ear and hearing disorders. It addresses hearing loss. First activities, connected with the World Hearing Day, took place in 2007, after the Beijing Declaration during the 1st International Conference on Prevention and Rehabilitation of Hearing Loss.ConclusionsLegislative measures are need to be undertaken to stress even further the importance of proper hearing. In the era of COVID-19 pandemic and its proven consequences on the hearing and vestibular system, urgent measures for timely diagnostics, treatment and rehabilitation are more than ever needed

On the limited amplitude resolution of multipixel Geiger-mode APDs

The limited number of active pixels in a Geiger-mode Avalanche Photodiode (G-APD) results not only in a non-linearity but also in an additional fluctuation of its response. Both these effects are taken into account to calculate the amplitude resolution of an ideal G-APD, which is shown to be finite. As one of the consequences, the energy resolution of a scintillation detector based on a G-APD is shown to be limited to some minimum value defined by the number of pixels in the G-APD.Comment: 5 pages, 3 figure

Vestibular effects of diving

Over the last 45 years, recreational self-contained underwater breathing apparatus (SCUBA) diving as a leisure activity has increased in popularity. According to the Professional Association of Diving Instructors (PADI), more than 23 million diver certificates have been issued across the globe. Given the popularity of scuba diving, it is incumbent on every physician to know and understand the specific medical hazards and conditions associated with scuba diving. Although diving has become more accessible and the equipment is much safer now, diving still has its inherent dangers. Each year incidents occur, ranging from seasickness and sinus problems to heart conditions and mortality. More than 80% of all diving complications occur in the head and neck region. A number of studies have found that diving can lead to the development of vestibular disorders such as: Barotrauma, Decompression sickness, Otitis externa, Bilateral exostoses, Chronic sinusitis (barosinusitis), Serous tubotympanic catarrh, Tinnitus, Dizziness, Vertigo.The aim of this paper was to share our experience in the field of treating patients with different types of ENT disorders after or before a diving session. We briefly summarized the most important information for some of the disorders.We included in our study for a period of 12 years: a total of 24 patients (four females and 20 males), who dive. They were between 25 and 55 years of age. Some presented in clinics with an ENT disorder. 19 were professional, qualified divers, five (three males and two females) dove for the first time. On all 24 patients we performed: audiometry tests, Tympanometry tests, OAE, Static and dynamic vestibular tests, vHIT – in the last five years, otoscopy examination, dental check-ups.All divers – no matter professionalists or not – should follow these recommendations: a thorough prophylactic ENT check-up should be performed before an active diving session. Chronic ENT inflammations should be addressed in a timely manner. Divers should follow all instructions from the certified Diving Associations

Historical development of methods for diagnosis and treatment of OSA

Obstructive sleep apnea (OSA) has been known to mankind since ancient times. Medical  documents from 2000 years ago that have been found contain information describing severe snoring (apnea) characteristic of OSA. In order to obtain the information targeted research was carried out in the Scientific databases PubMed, Scopus, ScienceDirect, Web of Science. „History of OSA”, „CPAP”, „Polysomnography” keywords were used in for the search.The aim of this article is to present the historical development of methods for diagnosis and treatment of OSA. In 1981 Sullivan et al. published in the Lancet scientific paper on Obstructive Sleep Apnea “ Reversal of obstructive sleep apnea by continuous airway pressure applied through the nares “ . At the end of the XIX th century, the term “Pickwickian syndrome” was introduced in the medical literature. In 1965, the polysomnographic unit was created and for the first time, with the help of electronic device, sleep apnea was registered in patients. Eventually ambulatory sleep testing was introduced as an alternative to polysomnography. Apnea Graph is a new innovative ambulatory sleep analysis tool that identifies the location of snoring obstruction and OSA. It also determines the type of OSA. In 1981, the first CPAP for treatment OSA was created. Sullivan’s findings prove that CPAP is a very effective device for treating OSA