Measuring every particle's size from three-dimensional imaging experiments

Often experimentalists study colloidal suspensions that are nominally monodisperse. In reality these samples have a polydispersity of 4-10%. At the level of an individual particle, the consequences of this polydispersity are unknown as it is difficult to measure an individual particle size from microscopy. We propose a general method to estimate individual particle radii within a moderately concentrated colloidal suspension observed with confocal microscopy. We confirm the validity of our method by numerical simulations of four major systems: random close packing, colloidal gels, nominally monodisperse dense samples, and nominally binary dense samples. We then apply our method to experimental data, and demonstrate the utility of this method with results from four case studies. In the first, we demonstrate that we can recover the full particle size distribution {\it in situ}. In the second, we show that accounting for particle size leads to more accurate structural information in a random close packed sample. In the third, we show that crystal nucleation occurs in locally monodisperse regions. In the fourth, we show that particle mobility in a dense sample is correlated to the local volume fraction.Comment: 7 pages, 5 figure

Fluids in cosmology

We review the role of fluids in cosmology by first introducing them in General Relativity and then by applying them to a FRW Universe's model. We describe how relativistic and non-relativistic components evolve in the background dynamics. We also introduce scalar fields to show that they are able to yield an inflationary dynamics at very early times (inflation) and late times (quintessence). Then, we proceed to study the thermodynamical properties of the fluids and, lastly, its perturbed kinematics. We make emphasis in the constrictions of parameters by recent cosmological probes.Comment: 34 pages, 4 figures, version accepted as invited review to the book "Computational and Experimental Fluid Mechanics with Applications to Physics, Engineering and the Environment". Version 2: typos corrected and references expande

Electronic and structural transitions in dense liquid sodium

At ambient conditions, the light alkali metals are free-electron-like crystals with a highly symmetric structure. However, they were found recently to exhibit unexpected complexity under pressure 1-6. It was predicted from theory 1.2 - and later confirmed by experiment 3-5 - that lithium and sodium undergo a sequence of symmetry-breaking transitions, driven by a Peierls mechanism, at high pressures. Measurements of the sodium melting curve 6 have subsequently revealed an unprecedented (and still unexplained) pressure-induced drop in melting temperature from 1,000 K at 30 GPa down to room temperature at 120 GPa. Here we report results from ab initio calculations that explain the unusual melting behaviour in dense sodium. We show that molten sodium undergoes a series of pressure-induced structural and electronic transitions, analogous to those observed in solid sodium but commencing at much lower pressure in the presence of liquid disorder. As pressure is increased, liquid sodium initially evolves by assuming a more compact local structure. However, a transition to a lower-coordinated liquid takes place at a pressure of around 65 GPa, accompanied by a threefold drop in electrical conductivity. This transition is driven by the opening of a pseudogap, at the Fermi level, in the electronic density of states - an effect that has not hitherto been observed in a liquid metal. The lower-coordinated liquid emerges at high temperatures and above the stability region of a close-packed free-electron-like metal. We predict that similar exotic behaviour is possible in other materials as well

A coherent study of emission lines from broadband photometry: specific star formation rates and [O iii]/Hβ ratio at 3 lt Z lt 6

We measure the Hα and [O iii] emission line properties as well as specific star formation rates (sSFRs) of spectroscopically confirmed 3 lt; z lt; 6 galaxies in COSMOS from their observed colors versus redshift evolution. Our model describes consistently the ensemble of galaxies including intrinsic properties (age, metallicity, star formation history), dust attenuation, and optical emission lines. We forward-model the measured Hα equivalent widths (EW) to obtain the sSFR out to z sim; 6 without stellar mass fitting. We find a strongly increasing rest-frame Hα EW that is flattening off above z sim; 2.5 with average EWs of 300-600 at z sim; 6. The sSFR is increasing proportionally to at z lt; 2.2 and to at higher redshifts, indicative of a fast build-up of mass in high-z galaxies within e-folding times of 100-200 Myr at z sim; 6. The redshift evolution at z gt; 3 cannot be fully explained in a picture of growth driven by cold accretion. We find a progressively increasing [O iii]λ5007/Hβ ratio out to z sim; 6, consistent with the ratios in local galaxies selected by increasing Hα EW (i.e., sSFR). This demonstrates the potential of using "local high-z analogs" to investigate the spectroscopic properties and relations of galaxies in the re-ionization epoch

Imaging of the acute scrotum: is there a place for contrast-enhanced ultrasonography?

Purpose: To present and evaluate the findings of contrast-enhanced ultrasonography (CEUS) in typical cases of acute painful scrotum. Materials and methods: Nineteen patients aged from 19 to 61 years old were included in the study. All patients underwent grey-scale and color Doppler ultrasonography (US) of the scrotum, followed by imaging after i.v. administration of 2.4 mL of a second generation ultrasound contrast agent (microbubbles of sulphur hexafluoride). A dedicated, contrast-sensitive technique was used (Contrast Tissue Imaging - CnTI). The diagnosis was confirmed surgically in 6 cases while in the remaining 8 cases it was based on the combination of clinical, imaging and laboratory findings. Results: The final diagnosis was testicular torsion (n = 4), epididymitis (n = 2, one of the cases complicated by abscess), testicular abscess (n = 1), scrotal abscess (n = 1), testicular trauma of varying severity (n = 6). Five out of 19 cases were true negatives: neither clinical examination nor laboratory tests revealed any pathology. CEUS showed complete lack of enhancement in all cases of torsion, permitting a rapid and definitive diagnosis. In the cases of infection complicated by abscesses, CEUS delineated the lesions much better than the combination of B-mode/Color Doppler US. The severely traumatized testicles showed minimal, inhomogeneous or patchy enhancement, while cases of minor trauma showed no significant enhancement defects. Hematomas were presented as non-enhancing lesions. Conclusion: Generally, there was no advantage over Doppler US as has been previously shown. However, CEUS can be used supplementary to traditional Doppler US in the investigation of blunt testicular trauma especially when there is uncertainty in diagnosis after appropriate clinical and radiographic evaluations occurs. Further studies are required to clearly define the indications of this method

The COSMOS2015 galaxy stellar mass function

We measure the stellar mass function (SMF) and stellar mass density of galaxies in the COSMOS field up to z ~ 6. We select them in the near-IR bands of the COSMOS2015 catalogue, which includes ultra-deep photometry from UltraVISTA-DR2, SPLASH, and Subaru/Hyper Suprime-Cam. At z> 2.5 we use new precise photometric redshifts with error σ z = 0.03(1 + z) and an outlier fraction of 12%, estimated by means of the unique spectroscopic sample of COSMOS (~100 000 spectroscopic measurements in total, more than one thousand having robust z spec > 2.5). The increased exposure time in the DR2, along with our panchromatic detection strategy, allow us to improve the completeness at high z with respect to previous UltraVISTA catalogues (e.g. our sample is >75% complete at 10 10 ℳ and z = 5). We also identify passive galaxies through a robust colour-colour selection, extending their SMF estimate up to z = 4. Our work provides a comprehensive view of galaxy-stellar-mass assembly between z = 0.1 and 6, for the first time using consistent estimates across the entire redshift range. We fit these measurements with a Schechter function, correcting for Eddington bias. We compare the SMF fit with the halo mass function predicted from ΛCDM simulations, finding that at z> 3 both functions decline with a similar slope in thehigh-mass end. This feature could be explained assuming that mechanisms quenching star formation in massive haloes become less effective at high redshifts; however further work needs to be done to confirm this scenario. Concerning the SMF low-mass end, it shows a progressive steepening as it moves towards higher redshifts, with α decreasing from -1.47 +0.02-0.02 -1.47-0.02+0.02 at z ≃ 0.1 to -2.11 +0.30-0.13 -2.11-0.13+0.30 at z ≃ 5. This slope depends on the characterisation of the observational uncertainties, which is crucial to properly remove the Eddington bias. We show that there is currently no consensus on the method to quantify such errors: Different error models result in different best-fit Schechter parameters