O egzistenciji rezonantne nuklearne magnetske relaksakcije pomoću spin-rotacionih međudjelovanja u čvrstom tijelu

The temperature and frequency dependences of the nuclear spin-lattice relaxation times have been measured for a series of nearly spherical molecules both in the solid and in the liquid state, using a pulse technique. The same anomalous behaviour which was found before in SF6, SeF6 and TeF6 is now shown to occur in MoF6, WF8 , DF8 and solid white phosphorus in a certain temperature range, The results seem to indicate that spin-rotational interactions do operate in a relatively large number of molecular solids and liquids and open the possibility of studying correlation functions for the angular velocity of molecules in the solid by NMR techniques.Sa impulsnim nuklearnim magnetnim rezonantnim spektrometrom izmerene su temperaturne i frekventne zavisnosti longitudinalnih relaksacionih vremena spin-rešetka u nizu gotov sfero simetričih molekula kako u čvrstoj tako i u tečnoj fazi. Na osnovu rezultata može se zaključiti da je spin-rotaciona interakcija dominantan relaksacioni mehanizam u srazmerno velikom broju molekula kako u čvrstom tako i u tečnom stanju, što daje mogućnost izučavanja korelacionih funkcija za uglovnu brzinu molekula metodama NMR-a

O egzistenciji rezonantne nuklearne magnetske relaksakcije pomoću spin-rotacionih međudjelovanja u čvrstom tijelu

The temperature and frequency dependences of the nuclear spin-lattice relaxation times have been measured for a series of nearly spherical molecules both in the solid and in the liquid state, using a pulse technique. The same anomalous behaviour which was found before in SF6, SeF6 and TeF6 is now shown to occur in MoF6, WF8 , DF8 and solid white phosphorus in a certain temperature range, The results seem to indicate that spin-rotational interactions do operate in a relatively large number of molecular solids and liquids and open the possibility of studying correlation functions for the angular velocity of molecules in the solid by NMR techniques.Sa impulsnim nuklearnim magnetnim rezonantnim spektrometrom izmerene su temperaturne i frekventne zavisnosti longitudinalnih relaksacionih vremena spin-rešetka u nizu gotov sfero simetričih molekula kako u čvrstoj tako i u tečnoj fazi. Na osnovu rezultata može se zaključiti da je spin-rotaciona interakcija dominantan relaksacioni mehanizam u srazmerno velikom broju molekula kako u čvrstom tako i u tečnom stanju, što daje mogućnost izučavanja korelacionih funkcija za uglovnu brzinu molekula metodama NMR-a

Preliminary NMR Data of Ammonium Heptafluorozirconate

Some time ago, Pauling and Hampson1 investigated the room temperature crystal structure of ammon,ium heptafluorozirconate and found that the substance contained the ion (ZrF7 ) 3- and not (ZrF,y - and F - ions as suggested earlier.2 However, they were not able to assign all the atoms to definite positions in the unit cell and had to assum e some disorder in the orientation of the ZrF7 complexes

Nikola Vranješ, Na pragu vječnosti. Promišljanja o pastoralu umirućih, Glas Koncila, Zagreb, 2015.

Biogeochemical cycles of carbon, nutrients, and oxygen transmit mean states, trends and variations of the physical realm in coastal upwelling systems to their food webs and determine their role in regional budgets of greenhouse gases. This contribution focuses on biogeochemical processes in the northern Benguela Upwelling System (NBUS), where low oxygen levels in upwelling source water are a major influence on carbon and nutrient cycles. Based on measurements during numerous expeditions and results of 3-D regional ecosystem modeling (project GENUS; Geochemistry and Ecology of the Namibian Upwelling System) we here examine source water character, effects of low oxygen conditions on nutrient masses and ratios, and of diazotrophic N2-fixation on productivity of the system and its transition to the adjacent eastern South Atlantic. In available observations, the effects of denitrification in water and sediment and phosphate release from sediments are minor influences on nitrate:phosphate ratios of the system, and excess phosphate in aged upwelling water is inherited from upwelling source water. Contrary to expectation and model results, the low N:P ratios do not trigger diazotrophic N2-fixation in the fringes of the upwelling system, possibly due to a lack of seeding populations of Trichodesmium. We also examine the flux of carbon from the sea surface to either sediment, the adjacent sub-thermocline ocean, or to regenerated nutrients and CO2. Observed fluxes out of the surface mixed layer are significantly below modeled fluxes, and suggest that regeneration of nutrients and CO2 is unusually intense in the mixed layer. This contributes to very high fluxes of CO2 from the ocean to the regional atmosphere, which is not compensated for by N2-fixation. Based on observations, the NBUS thus is a significant net CO2 source (estimated at 14.8 Tg C a− 1), whereas the CO2 balance is closed by N2-fixation in the model. Methane concentrations were low in surface waters in on-line measurements during 1 expedition, and based on these our estimate for the emission of methane for the entire Benguela system is below 0.2 Tg CH4 a− 1

Deglacial and Holocene sea-ice and climate dynamics in the Bransfield Strait, northern Antarctic Peninsula

The reconstruction of past sea-ice distribution in the Southern Ocean is crucial for an improved understanding of ice–ocean–atmosphere feedbacks and the evaluation of Earth system and Antarctic ice sheet models. The Antarctic Peninsula (AP) has been experiencing a warming since the start of regular monitoring of the atmospheric temperature in the 1950s. The associated decrease in sea-ice cover contrasts the trend of growing sea-ice extent in East Antarctica. To reveal the long-term sea-ice history at the northern Antarctic Peninsula (NAP) under changing climate conditions, we examined a marine sediment core from the eastern basin of the Bransfield Strait covering the last Deglacial and the Holocene. For sea-ice reconstructions, we focused on the specific sea-ice biomarker lipid IPSO25, a highly branched isoprenoid (HBI), and sea-ice diatoms, whereas a phytoplankton-derived HBI triene (C25:3) and warmer open-ocean diatom assemblages reflect predominantly ice-free conditions. We further reconstruct ocean temperatures using glycerol dialkyl glycerol tetraethers (GDGTs) and diatom assemblages and compare our sea-ice and temperature records with published marine sediment and ice core data. A maximum ice cover is observed during the Antarctic Cold Reversal 13 800–13 000 years before present (13.8–13 ka), while seasonally ice-free conditions permitting (summer) phytoplankton productivity are reconstructed for the late Deglacial and the Early Holocene from 13 to 8.3 ka. An overall decreasing sea-ice trend throughout the Middle Holocene coincides with summer ocean warming and increasing phytoplankton productivity. The Late Holocene is characterized by highly variable winter sea-ice concentrations and a sustained decline in the duration and/or concentration of spring sea ice. Overall diverging trends in GDGT-based TEX86L and RI-OH' subsurface ocean temperatures (SOTs) are found to be linked to opposing spring and summer insolation trends, respectively.</p

Preliminary NMR Data of Ammonium Heptafluorozirconate

Some time ago, Pauling and Hampson1 investigated the room temperature crystal structure of ammon,ium heptafluorozirconate and found that the substance contained the ion (ZrF7 ) 3- and not (ZrF,y - and F - ions as suggested earlier.2 However, they were not able to assign all the atoms to definite positions in the unit cell and had to assum e some disorder in the orientation of the ZrF7 complexes

Finger-like lysing patterns of blood clots.

One-dimensional modeling of fibrinolysis (Senf, 1979; Zidansek and Blinc, 1991; Diamond and Anand, 1993) has accounted for the dissolution velocity, but the shape of the lysing patterns can be explained only by two- or three- drug-induced blood clot dissolution patterns obtained by proton nuclear magnetic resonance imaging, which can be described by the enzyme transport-limited system of fibrinolytic chemical equations with diffusion and perfusion terms (Zidansek and Blinc, 1991) in the reaction time approximation if the random character of gel porosity is taken into account. A two-dimensional calculation based on the Hele-Shaw random walk models (Kadanoff, 1985; Liang, 1986) leads to fractal lysing patterns as, indeed, is observed. The fractal dimension of the experimental lysing patterns changes from 1.2 at the beginning of the experiments to a maximum of approximately 1.3 in the middle and then decreases toward one when the clot is recanalized