Mass entrainment rate of an ideal momentum turbulent round jet

We propose a two-phase-fluid model for a full-cone turbulent round jet that describes its dynamics in a simple but comprehensive manner with only the apex angle of the cone being a disposable parameter. The basic assumptions are that (i) the jet is statistically stationary and that (ii) it can be approximated by a mixture of two fluids with their phases in dynamic equilibrium. To derive the model, we impose conservation of the initial volume and total momentum fluxes. Our model equations admit analytical solutions for the composite density and velocity of the two-phase fluid, both as functions of the distance from the nozzle, from which the dynamic pressure and the mass entrainment rate are calculated. Assuming a far-field approximation, we theoretically derive a constant entrainment rate coefficient solely in terms of the cone angle. Moreover, we carry out experiments for a single-phase turbulent air jet and show that the predictions of our model compare well with this and other experimental data of atomizing liquid jets.Comment: 17 pages, 10 figure

The new record of the spotted catfish Arius maculates (Thunberg 1792) from Persian Gulf, Iran

The species Arius maculates (Thunberg 1792) (Siluriformes, Ariidae) is recorded for the first time from the muddy shores of the inter-tidal zone of Bandar Abbas, Persian Gulf, Iran in February 2011. In this study, the morphological features of Arius maculates are described. This species has previously been recorded from Gulf of Oman to Indonesia, north to Japan (locality type). This finding considerably extends our knowledge of the distribution of Arius maculates

KORIŠTENJE KONTRACEPCIJE I SPOLNO PONAŠANJE STUDENATA U BOSNI I HERCEGOVINI

The aim of the study was to establish the parameters of sexual behavior and contraception use among full time male students in Bosnia and Herzegovina. In a prospective study that included 2128 male students aged 19-24, an anonymous survey was conducted on sexual behavior and contraception use in four university cities in Bosnia and Herzegovina during the 2007-2009 period. Out of the total number of surveyed students (N=2118), 74.6% (n=1581) were sexually active and the largest number of students (16.7%, n=614) had sexual relations with one partner. In the group of subjects with one sex partner, there was a signifi cant difference according to universities (Cilj rada je defi nirati parametre spolnog ponašanja i upotrebu metoda kontracepcije kod redovnih studenata u BiH. Ispitanici i metode: U prospektivnoj studiji na 2.128 redovnih studenata, u dobi od 19 do 24. godine života provedena je anonimna anketa o spolnom ponašanju i korištenju kontracepcije u 4 univerzitetska grada u BiH u razdoblju od 2007. do 2009. god. Rezultati: Od ukupnog broja anketiranih studenata (N=2.118) spolno aktivnih je bilo 74,6 % (N=1.581), a najveći broj studenata - 16,7 % (N=614) imao je spolne odnose s jednim partnerom. U proporciji ispitanika s jednim spolnim partnerom postoji značajna razlika po univerzitetima za muške ispitanike (x2=13,62; p=0,009). Ne postoji značajna razlika u broju spolnih partnera studenata prema studijskim skupinama, prema proporciji ispitanika s jednim i dva partnera (x2=1,41; p=0,492), ali postoji značajna razlika po godinama studija studenata muškaraca (x2=10,13; p=0,038). Srednja dob seksarhe je 17,35±1,71 godina, te postoji statistički značajna razlika srednjih vrijednosti seksarhe (F(4,1576)=9,273; p<0,001). Kontracepciju je koristilo 74,3 % spolno aktivnih studenata. Kondom kao metodu kontracepcije koristili su u 79% (N=1249) slučajeva, a druge metode u 21 % (N=332) slučajeva. Zaključak: Porast spolne aktivnosti među studentima muškog spola registriran je uz visoku stopu korištenja kontracepcije tijekom spolnog odnosa

KORIŠTENJE KONTRACEPCIJE I SPOLNO PONAŠANJE STUDENATA U BOSNI I HERCEGOVINI

The aim of the study was to establish the parameters of sexual behavior and contraception use among full time male students in Bosnia and Herzegovina. In a prospective study that included 2128 male students aged 19-24, an anonymous survey was conducted on sexual behavior and contraception use in four university cities in Bosnia and Herzegovina during the 2007-2009 period. Out of the total number of surveyed students (N=2118), 74.6% (n=1581) were sexually active and the largest number of students (16.7%, n=614) had sexual relations with one partner. In the group of subjects with one sex partner, there was a signifi cant difference according to universities (Cilj rada je defi nirati parametre spolnog ponašanja i upotrebu metoda kontracepcije kod redovnih studenata u BiH. Ispitanici i metode: U prospektivnoj studiji na 2.128 redovnih studenata, u dobi od 19 do 24. godine života provedena je anonimna anketa o spolnom ponašanju i korištenju kontracepcije u 4 univerzitetska grada u BiH u razdoblju od 2007. do 2009. god. Rezultati: Od ukupnog broja anketiranih studenata (N=2.118) spolno aktivnih je bilo 74,6 % (N=1.581), a najveći broj studenata - 16,7 % (N=614) imao je spolne odnose s jednim partnerom. U proporciji ispitanika s jednim spolnim partnerom postoji značajna razlika po univerzitetima za muške ispitanike (x2=13,62; p=0,009). Ne postoji značajna razlika u broju spolnih partnera studenata prema studijskim skupinama, prema proporciji ispitanika s jednim i dva partnera (x2=1,41; p=0,492), ali postoji značajna razlika po godinama studija studenata muškaraca (x2=10,13; p=0,038). Srednja dob seksarhe je 17,35±1,71 godina, te postoji statistički značajna razlika srednjih vrijednosti seksarhe (F(4,1576)=9,273; p<0,001). Kontracepciju je koristilo 74,3 % spolno aktivnih studenata. Kondom kao metodu kontracepcije koristili su u 79% (N=1249) slučajeva, a druge metode u 21 % (N=332) slučajeva. Zaključak: Porast spolne aktivnosti među studentima muškog spola registriran je uz visoku stopu korištenja kontracepcije tijekom spolnog odnosa

Combined proper orthogonal decompositions of orthogonal subspaces

We present a method for combining proper orthogonal decomposition (POD) bases optimized with respect to different norms into a single complete basis. We produce a basis combining decompositions optimized with respect to turbulent kinetic energy (TKE) and dissipation rate. The method consists of projecting a data set into the subspace spanned by the lowest several TKE optimized POD modes, followed by decomposing the complementary component of the data set using dissipation optimized POD velocity modes. The method can be fine-tuned by varying the number of TKE optimized modes, and may be generalized to accommodate any combination of decompositions. We show that the combined basis reduces the degree of non-orthogonality compared to dissipation optimized velocity modes. The convergence rate of the combined modal reconstruction of the TKE production is shown to exceed that of the energy and dissipation based decompositions. This is achieved by utilizing the different spatial focuses of TKE and dissipation optimized decompositions.Comment: 9 pages, 3 figure

On the Discrepancies between POD and Fourier Modes on Aperiodic Domains

The application of Fourier analysis in combination with the Proper Orthogonal Decomposition (POD) is investigated. In this approach to turbulence decomposition, which has recently been termed Spectral POD (SPOD), Fourier modes are considered as solutions to the corresponding Fredholm integral equation of the second kind along homogeneous-periodic or homogeneous coordinates. In the present work, the notion that the POD modes formally converge to Fourier modes for increasing domain length is challenged. Numerical results indicate that the discrepancy between POD and Fourier modes along \textit{locally} translationally invariant coordinates is coupled to the Taylor macro/micro scale ratio (MMSR) of the kernel in question. Increasing discrepancies are observed for smaller MMSRs, which are characteristic of low Reynolds number flows. It is observed that the asymptotic convergence rate of the eigenspectrum matches the corresponding convergence rate of the exact analytical Fourier spectrum of the kernel in question - even for extremely small domains and small MMSRs where the corresponding DFT spectra suffer heavily from windowing effects. These results indicate that the accumulated discrepancies between POD and Fourier modes play a role in producing the spectral convergence rates expected from Fourier transforms of translationally invariant kernels on infinite domains