The Bernoulli levitation demonstration using a funnel and a ball is widely used to teach the Bernoulli principle. But the claim is made in the literature that there are other effects than the Bernoulli principle, and that solving the problem requires numerical fluid physics calculations. We measure the upward-acting force in such an experiment for a selection of balls with radii from 19.67 to 39.07 mm, and with weights from 0.037 to 0.159 N. We find that, when the ratio of the radius of the ball to radius of the inner opening of the funnel is greater than 2, and the ratio of ball radius is less than the wider opening of the funnel, the Bernoulli effect dominates.

In this study, oxidative stress and lipid peroxidation in honey bee larvae, pupae and the midguts of adult bees were investigated during a one-year exposure to radiofrequency electromagnetic fields (RF-EMFs) at a frequency of 900 MHz under field conditions. The experiment was carried out on honey bee colonies at three locations with electric field levels of 30 mV m−1, 70 mV m−1 and 1000 mV m−1. Antioxidant enzymes, glutathione-S-transferase (GST), catalase (CAT) and superoxide dismutase (SOD) and thiobarbituric acid reactive substances (TBARS) as indicators of lipid peroxidation were measured spectrophotometrically. The GST activity within the same developmental stage showed no significant differences regardless of electric field level or sampling time. The highest GST activity was found in the pupae, followed by activity in the larvae and midguts. Both CAT activity and TBARS concentration were the highest in the midguts, regardless of field level and sampling time. The larvae showed a significantly higher TBARS concentration at the location with an electric field level of 1000 mV m−1 compared to the locations with lower levels. Our results show that RF-EMFs at a frequency of 900 MHz can cause oxidative stress in honey bees, with the larval stage being more sensitive than the pupal stage, but there was no linear relationship between electric field level and effect in any of the developmental stages.

Siphons are devices that transport liquids uphill between two containers. It has been proposed that a siphon principle operates in closed circulatory systems, as best exemplified by the circulation of blood in mammals. This principle is supposed to ensure that no additional work is necessary to pump blood above the level of the heart, and that there is no gravitational static pressure gradient in the column of blood. The first statement is correct, while we demonstrate that, ignoring hydraulic resistance to blood flow, the static pressure gradient is equal to the hydrostatic gradient in a siphon model of blood circulation, although the details of the proof do not depend on the geometry of the circulatory system and the proof can be trivially extended to other models such as a vascular waterfall. This implies that the controversy over the siphon principle has no implications for the description of blood circulation, and that mechanisms such as the "baffle," which some authors have appealed to in order to obtain the expected gradient, are not necessary. In our discussion, we also discuss empirical data that appear to provide additional verification of our results, as well as several everyday occurrences that provide additional support.

The aim of this paper is to present the concept of entropy in a simple way and to show its key importance in the transport processes of ions through the cell membrane using the latest discoveries in biophysics. Using a real-life example, we show how processes within a system lead to an increase in entropy. We also show how this entropy increase is directly related to the irreversibility of the process, and how it defines the arrow of time (direction of the flow of time). Using an abstract example, we clarify the meaning of the concept of disorder in a system, which is often used in defining entropy by connecting it with the number of microstates that realise a macroscopic state of a system. The importance of entropy in transport processes of ions through the cell membrane is considered. We show that passive transport processes through the cell membrane are the result of an entropy increase in the cell membrane-transported substance system. A model of active ion transport through the cell membrane following Rubi et al. (2017) is presented. The force that transports ions through the channel in the transport protein arises due to the entropy gradient formed along the transport channel, which is a consequence of the funnel shape of the channel. The entropic force is proportional to the ratio of the ion-available cross-sections of the exit and entrance surface of the channel. That means that only a very funnel-shaped channel can produce a sufficiently large force on the ions to overcome the concentration gradient of the substance. We analyse the final result for the force of entropy in the limits of a very wide and very narrow channel and find that the entropic force is proportional to the ratio of the areas of the exit to entrance surfaces of the channel, i.e., when the channel is very wide, while it becomes high as the width of the channel tends to the ion diameter, i.e., when the channel is very narrow. We explicitly explain how the presented model solves several fundamental questions about the active transport of substances: how is energy, a scalar quantity, converted into the directional motion of the ion (a vector quantity), how does energy drive ions considering that the point of release of energy is far from the point of binding of an ion in a transport protein and finally, how does energy, which is released in a very limited space, transport the ions over a very large spatial scale.

We present a novel method for demonstrating the physical principles of ultrasound imaging at a level suitable for educational programmes up to the university level, using a simple mechanical model that is very inexpensive and accessible to a broad variety of educational institutions. The method revolves around the use of one or two steel springs that can be extended on a flat surface. The spring represents a tissue and the longitudinal wave traveling along the spring represents the propagation of an ultrasound wave in tissue. This method allows students to gain direct experience with wave propagation, reflection and transmission in tissue as well as insight into the physical processes underlying ultrasound imaging. These include equally the ultrasound diagnostic device measurement of the depth of various tissue boundaries, modelled as a simple measurement of the time elapsed between the emission of a wave and the detection of a wave reflected from an object intersecting the spring. An ultrasound device probes the boundary between a formation (an organ or a lesion) and surrounding tissue by registering the amplitude of reflection on the formation, which is proportional to a difference in acoustic impedance between the formation and the tissue. The amplitude of the reflected wave in our apparatus is also proportional to acoustic impedance between the spring and an object like a plastic ruler intersecting the spring, whose stiffness and consequently acoustic impedance can be adjusted by its offset. It is also easy to clearly see the reflected wave on the boundary of two coupled springs (two tissues) with different acoustic impedances. We represent a series of representative measurements using our mechanical model demonstrating its good precision.

Cilj je ovoga rada povezivanje temeljnih karakteristika tkiva s rezultatima dobivenim na rendgenskoj slici, analizirajući fizikalne principe interakcije koje vode do atenuacije rendgenskih fotona u tkivu. Na slikovitom primjeru dokazujemo da nećemo moći imati superdijagnostički uređaj koji bi mogao zamijeniti sve moderne i buduće dijagnostičke uređaje. Svakase tehnika oslikavanja tkiva temelji na jedinstvenim fizikalnim principima te stoga ona vidi točno određene kakateristike tkiva koja drugi dijagnostički uređaji (tehnike) ne mogu vidjeti. Oslikavanje se rendgenskim uređajem temelji na atenuaciji (slabljenju) snopa rendgenskih zraka nakon prolaska kroz tkivo. Glavni su mehanizmi interakcije rendgenskih fotona i tkiva fotoelektrični efekt (potpuna apsorpcija energije fotona) te Comptonovo raspršenje (djelomična apsorpcija energije fotona). Fotoelektrični efekt dominira na niskim i djelomično srednjim energijama i s povećanjem energije jako slabi, dok na srednjim i višim energijama dominira Comptonovo raspršenje. Analizom oba raspršenja, nakon dekompozicije linearnoga koeficijenta atenuacije na uobičajene fizikalne veličine, nalazimo da u režimu Comptonovoga raspršenja kontrast na slici je određen razlikama u gustoći tkiva, a u režimu fotoelektričnoga efekta ovisi o gustoći tkiva te snažno o rednom broju elemenata od kojih je tkivo sastavljeno. U radu su grafički prikazane vrijednosti kontrasta na rendgenskoj slici za osnovne tvorbe i tkiva i opisane njihove karakteristike, gustoća i redni broj elemenata od kojih su sastavljeni. Kompjuterizirana tomografija (CT) vidi potpuno iste karakteristike tkiva kao i klasična rendgenska tehnika. U radu je na eksplicitnom dvodimenzionalnom primjeru objašnjen princip komjuterizirane tomografije. On se temelji na zamišljenoj podjeli tkiva na male volumene (voksele) i snimanju tkiva iz više pozicija, pri čemu se za svaku poziciju postavljaju jednadžbe za apsorpciju zračenja. U dobivenom sustavu jednadžbi nepoznate vrijednosti su vrijednosti linearnog koeficijenta atenuacije za svaki voksel, koje se odrede numeričkim rješavanjem sustava jednadžbi, i prikažu na prikladnoj skali boja u trodimenzionalnom prikazu.

Exposure to radiofrequency electromagnetic fields (RF-EMF) at the operating frequencies of different communication devices can cause various biological effects. However, there is a lack of studies on the oxidative stress response and genotoxicity in the honey bee (Apis mellifera) after exposure to RF-EMF. In this study, we investigated the oxidative stress and DNA damage in honey bee larvae situated in waxcomb cells, exposed to modulated RF-EMF 23 Vm-1. The glutathione S-transferase activity decreased, whereas the catalase activity increased significantly in the honey bee larvae upon RF-EMF exposure. Superoxide dismutase activity, the level of lipid peroxidation, and DNA damage were not statistically altered in exposed honey bee larvae when compared to the control group. These results suggest that the biological effects of modulated RF-EMF in honey bee larvae depend on the exposure design.

We conducted a survey on the beekeeping production, practices and attitudes of 117 beekeepers in Croatia, via a questionnaire. The beekeepers were divided into three groups: full-time (professionals), part-time (side-liners) and hobby (hobbyists) beekeepers. The questions covered the purpose and size of their beekeeping production, the production interests of the beekeepers, treatment of the economically most important honeybee diseases, and the possibilities of the growth of their operation. Professional beekeepers were the youngest (39 years of age on average), with the largest average number of beehives per beekeeper (135 beehives), the largest proportion of LR hives and migratory apiaries, and the largest yearly per hive production of 17.04 kg of honey. The results show that the most marketable beekeeping product was honey, and that professional beekeepers also value propolis as equally interesting for production. They all inherited their beekeeping operations from their predecessors. Varroosis is perceived as the largest cause of honeybee colony death, followed by bad beekeeping practices. About 56% of the beekeepers are prepared to switch to organic/ecological beekeeping. Almost all the beekeepers (96.46%) support the introduction of the early diagnostics of American foulbrood. We found that professional beekeepers prefer the conservative economic model of growth based on their own equity, while hobbyists prefer a more expansive but riskier model of growth based on financial leverage (debt). Professional beekeepers are not inclined to create a mutual beekeepers' fund to cover losses. On the other hand, they strongly support the idea of creating an alliance for the purpose of joint market penetration.

In the survey, some variables were analyzed of cross-compliance control on livestock production farms in Croatia from 2011 to 2018. Collected data covered three animal production groups: cattle, sheep and goats, and pigs, for which the following parameters were monitored: wrongly marked breed, wrong gender, incorrect labeling, no animal on the holding, and no evidence of the animal in the farm register or in the national one. A total of 621,146 animals were surveyed, and in 92,523 (14.89%) of them noncompliance was found. It ranged from 9.66% in 2012 to 26.30% in 2018. Out of 221,311 investigated cattle, 373,515 sheep and goats and 26,320 pigs, noncompliance was found in 18.74%, 13.28% and 5.58% respectively. More noncompliance was detected in 2011 when the on-the-spot control started, followed by a decrease in the amount of noncompliance observed in 2012. However, in 2013, 2014 and 2018 an increase in the proportion of noncompliance was detected (17.54%, 16.86% and 26.30% respectively), due to the introduction of new parameters, i.e. new risk factors used in monitoring, and a lack of adequate education of farmers to adapt to new conditions. The value of the correlation coefficient (r) between the proportion of a particular production group of animals in the total number of animals, and the proportion of non-compliant animals in that production group for cattle was -0.232, for sheep and goats 0.637, and for pigs -0.317. For cattle and pigs this implies a negative but very weak correlation, and for sheep and goats a positive but moderate correlation. This means that there is not sufficient evidence of a strong negative correlation between those two variables, which was the hypothesis. The most important noncompliance item in cattle was no identification in the central register (26.25%), and the wrong gender (25.00%) in sheep and goats. The findings imply that more frequent training, as well as improvement of cooperation between all stakeholders should be obligatory measures for better farm management, resulting in reduced frequency of noncompliance.

Od početka svjetske gospodarske recesije 2008. godine pa i uoči nje, praćene su promjene gospodarskih pokazatelja u veterinarskim stanicama i ambulantama. Neki autori su u nekoliko navrata pisali o potencijalnim uzrocima i posljedicama krize na poslovanje veterinarskih organizacija. U žarištu interesa bilo je više pokazatelja od kojih su tri praćena u ovom istraživanju. To su: prosječna neto plaća, broj zaposlenih i ukupni prihod. Oni su prikazani za razdoblje od 2003. do 2017. godine. Radi stjecanja jasnijeg uvida u okolnosti u kojima su poslovale, našu smo pažnju proširili i na općenitije pokazatelje gospodarske aktivnosti na razini ukupnog gospodarstva (bruto domaći proizvod, jav- ni dug, zaposlenost, broj i dobna struktura stanovništva, uvoz i izvoz) i poljoprivrede kao bitne odrednice aktivnosti veterinarskih organizacija. Naime, rezultati istraživanja pojedinih autora pokazuju da je recesija više naštetila veterinarstvu negoli ukupnom gospodarstvu pa smo željeli u široj ekonomskoj slici uočiti naznake buduće gospodarske stvarnosti i upozoriti na njih. S obzirom na to da su gospodarski trendovi potaknuti i vođeni potrebama ljudi, demografski podatci mogu pomoći pri otkrivanju makro i mikro trendova. Zato smo u promatranje uključili i demografske pokazatelje. Ukupni prihod i broj zaposlenih u veterinarskim stanicama smanjivali su se, dok su plaće lagano rasle do 2008. a zatim stagnirale. U veteri- narskim ambulantama, za razliku od stanica, svi pokazatelji su rasli, no u godinama nakon početka recesije plaće su uglavnom stagnirale ili lagano padale. U 2017. godini zabilježen je lagani porast neto plaća i u veterinarskim stanicama i u veterinarskim ambulantama. Zabilježene promjene u kretanju poljoprivrednih i općih demografskih i gospodarskih trendova poput: bitnog smanjenja broja reproduktivnih životinja i proizvodnje mlijeka i jaja, starenja ljudske populacije i smanjenja nataliteta, stalno rastućeg uvoza hrane i pića i uvoza općenito te uočena jaka korelacija između duga i broja stanovnika, i rastući pritisak na novo zaduživanje upućuju na izvjesnu daljnju stagnaciju ili smanjivanje gospodarskih aktivnosti veterinarskih organizacija. Porast proizvodnje bio je najizraženiji u broju košnica i proizvonji meda, u uzgoju ovaca i konja te tovu pilića. Evidentno je da su se najviše smanjivale one stočarske proivodnje koje zahtijevaju više vještine, potrošenog vremena i intenzivnijeg rada, dok su porasle one koje traže manje rada i jednostavnije postupke. Struktura proizvodnje prilagođavala se potrebama i mogućnostima koje proizlaze iz strurkture radne snage.

The employment of veterinarians is an indicator of economic development and of the quality of the relationship between humans and nature. Several authors have published reports on the employment of veterinarians. This paper examines the trends in unemployment and employment of veterinarians according to the records of the Croatian Employment Service (CES) in the period from 2010 to 2019. The CES is a public institution of the Republic of Croatia established under the Labour Market Act (Official Gazette 118/18) that plays a key role in regulating supply and demand on the labour market of the Republic of Croatia. The average number of employed veterinarians was higher than the average number of veterinarians registered in the CES records. An average of 181 veterinarians were sought annually, 160 were employed and 143 were registered, indicating that demand surpassed supply. Veterinarians were recruited faster than the average person with a college degree, within 180 days, and very few were in longterm unemployment. Most were employed in the category of young people (up to 30 years of age), and most were employed without any previous work experience. More women than men were employed. Most veterinarians were employed in the City of Zagreb, which reflects the relatively low livestock production and depopulation of rural areas, as the traditionally main and safest source of employment for veterinarians. According to the National Classification of Economic Activities (NKD), veterinarians were employed in almost all groups of activities, allowing for greater employment flexibility and mobility on the labour market. According to the National Classification of Occupations (NKZ), on the other hand, most veterinarians were employed in group 2 (experts and scientists), likely since veterinary medicine is a regulated profession. This also means that several were employed under their qualification levels. The employment of veterinarians was relatively better than for other university-educated workers, due to the relatively higher number of registered vacancies. The regression equation showed that the number of jobs offered to veterinarians in the observed period increased by slightly more than 9 jobs per year, indicating a possible increase in demand for veterinarians in the future. The same trend is seen in the projection of future trends in the labour market, which predicted an increase in the number of employed veterinarians in the period from 2014 to 2020, as well as an increase in the number of retirements. The data imply that it is necessary to increase the number of veterinarians, but also to raise their competencies to meet the increased competition on the European and global labour markets.

The effects were measured of low-doses of gamma radiation within 24 hours after irradiation on the activity of glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), catalase (CAT) and levels_of glutathione (GSH) and lipid peroxide concentrations (malondialdehyde, MDA) in embryonic chick liver. The chick embryos were irradiated with doses of gamma radiation of 0.05, 0.15,0.3, 0.5 and 0.8 Gy at the dose rate of 0.0117 Gy/s on day 19 of incubation. All parameters were measured 1, 3, 6, 12 and 24 hours after irradiation by spectrophotometry, apart from the level of lipid peroxidation, which was assessed using high performance liquid chromatography (HPLC). A versatile analysis of the data was made and it consisted of: 1) a comparison of the means of antioxidant enzyme activities and GSH and MDA concentrations for each radiation dose and the time after irradiation with the corresponding control samples; 2) research into the temporal dynamics of enzyme activities and concentrations a) for each value of radiation dose and b) when the data for radiation doses were merged, i.e. regardless of the radiation doses. A significant increase in GSH-Px activities in time after irradiation was found in dose intervals from 0.05 to 0.5 Gy, which was well described by linear function. This is a highly reliable result, because it was obtained as a result of all the analyses applied. For other parameters, we did not find any dependence of activities and concentrations on time. The analysis of comparison of means of the irradiated and control samples gave statistically significant results for some dose-time pairs.

It has been documented that low-dose ionising irradiation enhance the immune response on both cellular and humoral immunity in mammals. In the present study three experiments were conducted to compare antibody titre against a vaccinal strain of Newcastle disease virus after low-dose total body gamma irradiation in chickens. In all experiments, male Leghorn chicks were irradiated, on day 1 or 3 of life, with the dose of 0.05, 0.15, 0.30, 0.50 and 0.80 Gy gamma radiation. In two experiments, after irradiation, chicks were vaccinated with the commercial Newcastle disease vaccine by the nebulisation method. Blood samples were collected for serological analyses from day one or 7 up to day 28 in weekly intervals, depending on experimental design. Specific serum anti-Newcastle disease virus antibodies were quantitated by haemagglutination inhibition assay. No significant effect on the level of haemagglutination inhibition of maternal antibody titre and antibody titre against vaccinal Newcastle disease virus as well as on the rate of antibody catabolism was found. The ionising radiation used in the present experiment did not influence the humoral immune response in this light strain of chickens.

The nuclear structure of the semi-magic isotope Sn-125 was investigated by means of the Sn-124(n(th), gamma gamma)Sn-125 reaction and the Sn-124((d) over right arrow, p)Sn-125 reaction. More than 400 levels, in most cases with their spin, parity, (d, p) spectroscopic factor, and gamma decay, were identified. About 750 gamma transitions from our (n, gamma gamma) experiment form the essentially complete gamma-decay scheme following thermal neutron capture. Using this extensive gamma-decay scheme the neutron binding energy was determined to be 5733.5(2) keV. The strong correlation of the (d, p) strengths and the (n, gamma) intensities for more than 50 levels gives evidence for the direct neutron capture process, which was studied in detail. The experimental data were compared with predictions of the quasiparticle phonon model.

Two-photon decay has been extensively studied in atomic, nuclear and particle physics since the 1930s when the problem of stability of the 2s state of the hydrogen atom emerged. Since then, many theoretical and experimental investigations have been made on hydrogen and one-electron (H-like) ions and on helium and two-electron (He-like) ions. The work on two-photon decay in many-electron systems involving inner shells started about 30 years ago and, in the meantime, two-photon decay of the K-shell vacancy state has been the subject of many theoretical and experimental studies. Experimental results have been obtained for 2s→1s and higher-state electron →1s two-photon transitions in molybdenum, and for 2s → 1s, 3s → 1s, 3d → 1s and 4sd → 1s two-photon transitions in silver, xenon, hafnium and mercury. Nonrelativistic and relativistic calculations of the processes have been made. The relativistic calculations for transitions in molybdenum, silver and xenon atoms are in a reasonable agreement with the experimental results, but some problems remain to be solved. A review of investigations of two-photon transitions in atomic systems is presented.

A review of results of the new method for measuring the Compton scattering on bound electrons in germanium, introduced by the presented authors, is given. It is based on the application of two detectors that operate in the coincidence mode. One detector is used as the scatterer and the other as the detector of scattered radiation. Two conditions, simultaneity of pulses from the two detectors and constant energy sum, result in very clean spectra in broad energy regions. Normalization of the Compton spectra to the Ge K X-ray escape peaks, which are measured simultaneously with the Compton spectrum, gives reliable double-differential Compton-scattering cross sections on an absolute scale. Several versions of the impulse approximation are compared to the cross sections obtained by the present method for incident photon energies in the range from 60 to 105keV. The non-relativistic impulse approximation gives the best agreement to the experimental data. We point out the suitability of the new method for an investigation of the incoherent scattering function at small photon momentum transfer.

In a previous study of our group, it has been shown that broad continua adjacent to the full-energy peaks (the “shoulders”) in the spectra of 59.537keV γ-rays emitted from a standard Am241 calibration source are due to Compton scattering of γ-rays in the source plate (mass of only 0.59g). An extension of that work is presented with the aim to show that the analogous shoulder spectra also appear in the K X-ray fluorescence spectra, and are due to the Compton scattering of fluorescence radiation in the target. The experimental set-up was carefully designed with the aim to strongly reduce single and double scattering of Am241 radiation from all surrounding materials except from the targets. An Am241 annular source was used to excite the fluorescence radiation. Measurements have been made with a target of parafine loaded with Ce2O3 and, for comparison, with a pure parafine target. To show that Compton scattering is the main cause of the observed shoulder spectra, the measurements were made for three orientations of the targets with respect to the detector-to-target centre-line. The observed changes in the measured spectra clearly show that the shoulders are mainly due to Compton scattering in the targets. Calculations of the shoulder spectra show a good agreement to the measured spectra.

A study was made of the continuum adjacent to the K-alpha 1 and K-alpha 2 peaks (the 'shoulder') in lanthanum fluorescence spectra. The fluorescence was induced by 59.537 keV gamma-rays from a Am-241 source. The spectra were observed with an La2O3-loaded paraffin target (the 'La target'). To limit the observations to the scattering in the target, a collimator was used in front of the germanium detector, which strongly reduced the near-detector scattering. Changes in the shoulder spectra were observed on attaching additional mass to the La target and on changing its orientation with respect to the detector-to-target centre-line. The measurements clearly show that the main cause of the shoulder spectra is the in-target Compton scattering. A different distribution of mass in the vicinity of the fluorescing atoms with respect to the detector-to-target centre-line results in different probabilities of the observed scattering at all angles. Since the energy of secondary Compton photons is directly related to the scattering angles, different distributions of mass cause changes in the shoulder spectra. Comparison of the calculated and measured shoulder spectra shows good agreement on an absolute scale. Copyright (c) 2006 John Wiley & Sons, Ltd.

A considerable reduction of background and an improvement of spectra of low-energy γ-rays, measured with a planar high-purity Ge detector, has been achieved using a small source and a careful design of collimators and shielding. The aim of the design was to reduce strongly the detection of scattered radiation. The design of the shielding was based on previous studies by the present authors of effects of near-source scattering on photon spectra. That work has shown the effects of different distribution of mass around the γ-ray emitting atoms, seen as continuous distributions adjacent to the full-energy peaks (the “shoulders”). In the present measurement, reduction of intensity of the shoulders by as much as a factor of 10 has been achieved. The calculated shoulder spectra reproduce well the measured ones. Since a much lower background was achieved (peak-to-shoulder height ratio of about 2500), the shape of the full-energy peak could be analysed in a broader range. Deviations from the Gaussian shape have not been observed in the range ±3.4σ about the midpoint of the peak. The calculated shoulder spectrum, which is dominated by scattering in the source, and the Gaussian peak represent the measured spectrum in their energy range very well, so that less than 0.1% of counts are not accounted for. Present arrangements offer improved searches for lines of weak intensity and more accurate determination of peak intensities in X-ray and low-energy γ-ray spectra.