Parabolic tendons in prestressed concrete - how accurate are equivalent loads?

The mechanical effects of a parabolic tendon can be modeled replacing the tendon by external loads applied to the concrete. The intensity of these loads depends on the prestressing force P and curvature of the tendons. These two factors are also interrelated because the losses of prestress vary with the curvature. The structural analysis can be simplified by approximating that the line load against the tendon, able to maintain the initial parabolic form of the tendon and called equivalent load, is constant, perpendicular to the centroidal axis of the beam and equal to P/R where R is the radius of curvature of the parabola at its vertex. This approximation is one of the key issues in the textbooks but normally not properly justified. In this paper, the mathematical background for the approximation is formulated. Some typical tendon layouts are analyzed to evaluate the approximation error. The error proved to be insignificant for simple beams. For cantilever and continuous beams more accurate methods in the final design are recommended.

Vibrational analysis of nanoplate with surface irregularity via Kirchhoff plate theory

In this work, an attempt is done to apply the Kirchhoff plate theory to find out the vibrational analyses of a nanoplate incorporating surface irregularity effects. The effects of surface irregularity on natural frequency of vibration of nanomaterials, especially for nanoplates, have not been investigated before, and most of the previous research have been carried for regular nanoplates. Therefore, it must be emphasized that the vibrations of irregular nanoplate are novel and applicable for the nanodevices, in which nanoplates act as the main structure of the nanocomposite. The surface irregularity is assumed in the parabolic form at the surface of the nanoplate. A novel equation of motion and frequency equation is derived. The obtained results provide a better representation of the vibration behavior of irregular nanoplates. It has been observed that the presence of surface irregularity affects considerably on the natural frequency of vibrational nanoplates. In addition, it has been seen that the natural frequency of nanoplate decreases with the increase of surface irregularity parameter. Finally, it can be concluded that the present results may serve as useful references for the application and design of nano-oscillators and nanodevices, in which nanoplates act as the most prevalent nanocomposites structural element.

Determinants of the transition to upper secondary school: differences between immigrants and Italians

The determinants of the transition from lower secondary to upper secondary school of Italian and immigrant teenagers (16-19 age range) were identified joining the European Union Statistics on Income and Living Conditions (EU-SILC) and the Italian Survey on Income and Living Conditions of Families with Immigrants in Italy (IM-SILC) for 2009. A set of individual, family, and contextual characteristics was selected through the Lasso method and a Bayesian approach to explain the choice of upper secondary schooling (yes/no). The transition from the low secondary to upper secondary school showed a complex pattern involving many variables: compared to men, women did not prove to have any differences, many components of income entered the model in a parabolic form, education level and income of parents proved to be very important, as was their occupation. The contextual factors revealed their importance: the latter included the degree of urbanisation, the South macro-region, household tenure status, the amount of optional technological equipment, and so on. Differences between Italians and immigrants disappeared when family background and parental characteristics were taken into account.

On perturbation theory and critical exponents for self-similar systems

Gravitational critical collapse in the Einstein-axion-dilaton system is known to lead to continuous self-similar solutions characterized by the Choptuik critical exponent $$\gamma $$ γ . We complete the existing literature on the subject by computing the linear perturbation equations in the case where the axion-dilaton system assumes a parabolic form. Next, we solve the perturbation equations in a newly discovered self-similar solution in the hyperbolic case, which allows us to extract the Choptuik exponent. Our main result is that this exponent depends not only on the dimensions of spacetime but also the particular ansatz and the critical solutions that one started with.

The Effect of Temperature on the Spread of COVID-19

This study analyzes the findings about the spread of COVID-19 in regions of varying temperatures. This paper will use the analysis of public data to conclude how impactful temperature is in determining the spread of COVID-19. In addition, this paper will shed light on some trends and some historical relevance to other pandemics similar in genetic makeup and growth. There have been numerous claims that higher temperatures will cause COVID-19 to diminish quickly and die out during the summer months. Other viruses like the flu and influenza are more common, and they display signs of seasonality. For example, the flu occurs in the Fall and Winter months which is why people get vaccines or flu shots in the preceding months. The conclusion about temperature’s significance could also highlight the stage of severity of the virus. If the cases, start to drop for example, one could conclude that the virus is past its peak and will die out soon. Several states from the United States were monitored for their daily cases and temperature before being averaged into three-day intervals to depict a smoother trend. Both variables are public and accessible to all. The states were divided into colder states(New York, Pennsylvania, and Illinois) and hotter states(Texas, California, and Georgia). The results varied and displayed different trends. The colder states seemed to have gone past their peak and displayed a downward parabolic form. The temperature and cases displayed an inversely proportional relationship. The hotter states showed a constantly increasing case count with the graph showing a spike around the same time. The hotter states displayed an exponential trend and it is hard to predict when and how much they will peak. These two differing trends suggest that the effect temperature can have is not obvious across numerous areas. Therefore, temperature does not appear as a significantly impactful determinant in the growth of COVID-19.

Production process and the yield of hay Medicago sativa l. of the first year of life in rice crop rotation

The predecessors of rice, combined with their characteristic agricultural machinery, restore soil fertility, increase the yield of rice, provide forage products and as a result determine the productivity of the entire rotation of the crop rotation. In the rice crop rotations of the Sarpinsky lowland, studies are conducted to study the yield of alfalfa of the 1st year of life in the rice crop rotation on the reserves of productive moisture remaining after rice at different seeding rates. The soil cover of rice cheques is represented by brown semi-desert medium-and heavy-loamy soils in combination with saline. In the first year of the life of alfalfa (Medicago sativa L.) two residues of above-ground mass were obtained on residual moisture reserves (250–320 mm) after rice. The maximum yield of hay for two mowing 2.86-3.62 t/ha was obtained in the version with a seeding rate of 9.0 million pieces /ha, which is 0.86-1.21 t/ha more than the control option (5.0 million pcs/ha). It has been developed a dynamic model based on the yield of hay from alfalfa seeding rate seed having parabolic form with a maximum on top with a seeding rate of 9.0 million pcs/ha.

Numerical study of the influence of geometric form of chimney on the performance of a solar updraft tower power plant

Today, solar radiation is known as an important renewable energy which can be exploited in several ways such as solar updraft tower power plants, photovoltaic power plants, etc. In a solar updraft tower power plant, sunshine heats the air beneath a wide collector surrounding a tall tower and causes a hot air updraft in the tower by the chimney effect. This airflow drives wind turbines, placed almost in the chimney base, to produce electricity. In this study, the effect of the geometric form of the chimney on the performance of one solar updraft tower power plant is numerically investigated. Regarding the importance of the kinetic power of the hot air on power generation, it is intended to increase the air velocity by varying the forms of the chimney without changing the main dimensions of solar updraft tower power plant such as tower height and collector geometries. This approach may decrease the financial costs of the solar updraft tower power plant. For the numerical simulations, a finite volume computational fluid dynamics code solves the governing equations on an axisymmetric pi-shape domain (15° of whole geometry). To validate the results, the Manzanares solar updraft tower power plant experimental data are utilized. In this study, 15 forms of chimney based on a logical three-step procedure (from a basic cylindrical to a parabolic form) are examined. So, an appropriate/final form with a parabolic curve of chimney wall with divergence angle is obtained. Results indicate that the final form has the highest updraft air velocity. In fact, the average updraft air velocity increases from 15.66 m/s for the basic form to the value of 23.36 m/s (around 49.17% increments) for the final form.