Directing Min protein patterns with advective bulk flow

We theoretically predict and experimentally show that the propagation direction of in vitro Min protein patterns can be controlled by a hydrodynamic flow of the bulk solution. We find downstream propagation of Min wave patterns relative to the bulk flow direction for low MinE:MinD concentration ratios, but upstream propagation for large MinE:MinD ratios, with multistability of both propagation directions in between. A theoretical model for the Min system reveals the mechanism underlying the upstream propagation and links it to the fast conformational switching of MinE in the bulk. For high MinE:MinD ratios, upstream propagation can be reproduced by a reduced model in which increased MinD bulk concentrations on the upstream side promote protein attachment and hence, propagation in that direction. For low MinE:D ratios, downstream propagation is described by the minimal model, as additionally confirmed by experiments with a non-switching MinE mutant. No advection takes place on the membrane surface where the protein patterns form, but advective bulk flow shifts the protein-concentration profiles in the bulk relative to the membrane-bound pattern. From a broader perspective, differential flows in a bulk volume relative to a surface are a relevant general feature in bulk-surface coupled systems. Our study shows how such a differential flow can control surface-pattern propagation and demonstrates how the global pattern's response may depend on specific molecular features of the reaction kinetics.

Possible Observational Evidence for the Existence of a Parallel Universe

Many totally different kinds of astrophysical observations demonstrated that, in our universe, there exists a preferred direction. Specifically, from observations in a wide range of frequencies, the alignment of various preferred directions in different data sets was found. Moreover, the observed Cosmic Microwave Background (CMB) quadrupole, CMB octopole, radio and optical polarizations from distant sources also indicate the same preferred direction. While this hints at a gravitational pull from the “outside”, the observational data from the Plank satellite showed that the bulk flow velocity was relatively small: much smaller than was initially thought. In the present paper we propose a configuration where two three-dimensional universes (one of which is ours) are embedded in a four-dimensional space and rotate about their barycenter in such a way that the centrifugal force nearly (but not exactly) compensates their mutual gravitational pull. This would explain not only the existence of a preferred direction for each of the three-dimensional universes (the direction to the other universe), but also the fact that the bulk flow velocity, observed in our universe, is relatively small. We point out that this configuration could also explain the perplexing features of the Unidentified Aerial Phenomena (UAP), previously called Unidentified Flying Objects (UFOs), recorded by various detection systems—the features presented in the latest official report by the US Office of the Director of National Intelligence. Thus, the proposed configuration of the two rotating, parallel three-dimensional universes seems to explain both the variety of astrophysical observations and (perhaps) the observed features of the UAP.

Membrane Distillation: Pre-Treatment Effects on Fouling Dynamics

In the research reported in this paper, membrane distillation was employed to recover water from a concentrated saline petrochemical effluent. According to the results, the use of membrane distillation is technically feasible when pre-treatments are employed to mitigate fouling. A mathematical model was used to evaluate the fouling mechanism, showing that the deposition of particulate and precipitated material occurred in all tests; however, the fouling dynamic depends on the pre-treatment employed (filtration, or filtration associated with a pH adjustment). The deposit layer formed by particles is not cohesive, allowing its entrainment to the bulk flow. The precipitate fouling showed a minimal tendency to entrainment. Also, precipitate fouling served as a coupling agent among adjacent particles, increasing the fouling layer cohesion.

Cosmic Flow Measurement and Mock Sampling Algorithm of Cosmicflows-4 Tully−Fisher Catalog

Measurements of cosmic flows enable us to test whether cosmological models can accurately describe the evolution of the density field in the nearby universe. In this paper, we measure the low-order kinematic moments of the cosmic flow field, namely bulk flow and shear moments, using the Cosmicflows-4 Tully−Fisher catalog (CF4TF). To make accurate cosmological inferences with the CF4TF sample, it is important to make realistic mock catalogs. We present the mock sampling algorithm of CF4TF. These mocks can accurately realize the survey geometry and luminosity selection function, enabling researchers to explore how these systematics affect the measurements. These mocks can also be further used to estimate the covariance matrix and errors of the power spectrum and two-point correlation function in future work. In this paper, we use the mocks to test the cosmic flow estimator and find that the measurements are unbiased. The measured bulk flow in the local universe is 376 ± 23 (error) ± 183 (cosmic variance) km s−1 at depth d MLE = 35 Mpc h −1, to the Galactic direction of (l, b) = (298° ± 3°, −6° ± 3°). Both the measured bulk and shear moments are consistent with the concordance Λ Cold Dark Matter cosmological model predictions.

Gaussianization of peculiar velocities and bulk flow measurement

The line-of-sight peculiar velocities are good indicators of the gravitational fluctuation of the density field. Techniques have been developed to extract cosmological information from the peculiar velocities in order to test cosmological models. These techniques include measuring cosmic flow, measuring two-point correlation and power spectrum of the peculiar velocity fields, and reconstructing the density field using peculiar velocities. However, some measurements from these techniques are biased due to the non-Gaussianity of the estimated peculiar velocities. Therefore, we rely on the 2MTF survey to explore a power transform that can Gaussianize the estimated peculiar velocities. We find a tight linear relation between the transformation parameters and the measurement errors of log-distance ratio. To show an example for the implementation of Gaussianized peculiar velocities in cosmology, we develop a bulk flow estimator and estimate bulk flow from the Gaussianized peculiar velocities. We use 2MTF mocks to test the algorithm, and we find the algorithm yields unbiased measurements. We also find this technique gives smaller measurement errors compared to other techniques. In Galactic coordinates, at the depth of 30 h −1 Mpc, we measure a bulk flow of 332 ± 27 km s−1 in the direction (l,b) = (293° ± 5°, 13° ± 4°). The measurement is consistent with the ΛCDM prediction.

On the role and the implications of large-scale peculiar motions on the deceleration parameter of the universe

Κανένας ρεαλιστικός παρατηρητής δεν ακολουθεί την ομαλή διαστολή του σύμπαντος, την λεγόμενη «ροή Hubble», αλλά όλοι κινούμαστε ως προς αυτή. Ειδικότερα, ο Γαλαξίας μας και το τοπικό σμήνος γαλαξιών, κινούνται με ταχύτητα περίπου 600km/s. Επίσης, ένας μεγάλος αριθμός πρόσφατων ερευνών έχει επανειλημμένα επιβεβαιώσει την παρουσία ίδιων κινήσεων μεγάλης κλίμακας, τις επονομαζόμενες και «bulk flows». Παρόλα αυτά, οι ίδιες κινήσεις συνήθως παρακάμπτονται στις περισσότερες θεωρητικές κοσμολογικές μελέτες, ενώ στις ελάχιστες που συνυπολογίζονται η ανάλυση είναι σχεδόν αποκλειστικά Νευτώνεια. Επί πλέον, οι μελέτες γίνονται από τη σκοπιά του ιδεατού παρατηρητή, αυτού που ακολουθεί την ομαλή διαστολή Hubble, και όχι του πραγματικού που έχει μία σχετική ιδιοταχύτητα. Αυτό έχει ως αποτέλεσμα οι επιπτώσεις της ιδίας κίνησής του γαλαξία μας, ως προς την ομαλή διαστολή του σύμπαντος, να μην συνυπολογίζονται. Ωστόσο, είναι από καιρό γνωστό ότι φαινόμενα που συνδέονται με σχετική κίνηση επηρεάζουν τον τρόπο με τον οποίο οι παρατηρητές ερμηνεύουν το περιβάλλον τους. Μάλιστα, η ιστορία της αστρονομίας είναι γεμάτη παραδείγματα όπου η σχετική κίνηση έχει οδηγήσει σε καταφανή παρερμηνεία της πραγματικότητας. Ο σκοπός της συγκεκριμένης διατριβής είναι να προσφέρει μία σχετικιστική μελέτη των ίδιων κινήσεων και να ερευνήσει τις επιπτώσεις τους στον τρόπο με τον οποίο αντιλαμβανόμαστε τη μέση κινηματική συμπεριφορά του σύμπαντος που μας περιβάλει και πιο συγκεκριμένα τον ρυθμό επιτάχυνσης/επιβράδυνσης αυτού. Ο τελευταίος προσδιορίζεται από την παράμετρο επιβράδυνσης, η οποία παραδοσιακά είναι θετική όταν το σύμπαν επιβραδύνεται και αρνητική όταν επιταχύνεται. Εισάγοντας ένα «κεκλιμένο» (tilted) κοσμολογικό μοντέλο, επιτρέπουμε δύο οικογένειες παρατηρητών. Η πρώτη ακολουθεί την ομαλή ροή Hubble, η οποία ορίζει και το σύστημα αναφοράς του σύμπαντος, ενώ η δεύτερη οικογένεια ζει σε έναν τυπικό γαλαξία, όπως ο δικός μας (Milky Way), και κινείται ως προς την πρώτη. Θεωρώντας ότι το σύμπαν περιγράφεται από ένα διαταραγμένο κοσμολογικό μοντέλο Friedmann και υποθέτοντας ύλη με μηδενική πίεση, την επονομαζόμενη «σκόνη», δείξαμε ότι η παράμετρος επιβράδυνσης που μετρούν οι δύο παραπάνω παρατηρητές μπορεί να παίρνει αισθητά διαφορετική τιμή στα συστήματα αναφοράς τους και ότι η διαφορά αυτή οφείλεται αποκλειστικά και μόνο στη σχετική τους κίνηση. Επιπλέον, κάνοντας χρήση σχετικιστικής θεωρίας γραμμικών κοσμολογικών διαταραχών, δείξαμε ότι παρατηρητές που βρίσκονται εντός μίας ελαφρά συστελλόμενης bulk flow ενδέχεται να προσδίδουν αρνητικές τιμές στην δική τους, την τοπικά μετρούμενη, παράμετρο επιβράδυνσης, ενώ το σύμπαν σαν σύνολο να επιβραδύνεται. Αν και το γεγονός αυτό είναι τοπικό και οφείλεται αποκλειστικά στην ιδία κίνηση του παρατηρητή, οι περιοχές που επηρεάζονται είναι συνήθως αρκετά μεγάλες (από μερικές εκατοντάδες Mpc έως αρκετές εκατοντάδες Mpc), ώστε να δημιουργείται η λανθασμένη εντύπωση ότι ολόκληρο το σύμπαν έχει πρόσφατα περάσει σε φάση επιταχυνόμενης διαστολής. Ενδείξεις για την ορθότητα του παραπάνω σεναρίου και της πιθανότητας η πρόσφατη επιταχυνόμενη διαστολή του σύμπαντος να αποτελεί μία ψευδαίσθηση και ένα δημιούργημα της ιδίας κίνησης του γαλαξία μας, θα πρέπει να αναζητηθούν στα παρατηρησιακά δεδομένα. Αυτά, εκτός των άλλων, πρέπει να εμπεριέχουν την χαρακτηριστική υπογραφή, το «σήμα κατατεθέν», των ιδίων κινήσεων, δηλαδή μία φαινομενική (τύπου Doppler) διπολική ανισοτροπία που θα οφείλεται στην κίνηση του παρατηρητή. Με άλλα λόγια, στα παρατηρησιακά δεδομένα, το σύμπαν θα πρέπει να φαίνεται ότι επιταχύνεται ταχύτερα προς μία κατεύθυνση της ουράνιας σφαίρας και εξίσου βραδύτερα προς την αντιδιαμετρική. Τα τελευταία δέκα χρόνια υπάρχουν αρκετές αναφορές στη βιβλιογραφία ότι ένας διπολικός άξονας, όπως αυτός που προαναφέρθηκε, μπορεί πράγματι να υπάρχει στα δεδομένα των σουπερνόβα. Με άλλα λόγια, το σύμπαν μας μπορεί πράγματι να φαίνεται πως επιταχύνεται πιο γρήγορα προς μία κατεύθυνση στον ουρανό και εξίσου πιο αργά κατά μήκος του αντίποδα.

A NONHOMOGENEOUS BULK FLOW MODEL FOR GAS IN LIQUID FLOW ANNULAR SEALS: AN EFFORT TO PRODUCE ENGINEERING RESULTS

Seals in multiple phase rotordynamic pumps must operate without compromising system efficiency and stability. Both field operation and laboratory experiments show that seals supplied with a gas in liquid mixture (bubbly flow) can produce rotordynamic instability and excessive rotor vibrations. This paper advances a nonhomogeneous bulk flow model (NHBFM) for the prediction of the leakage and dynamic force coefficients of uniform clearance annular seals lubricated with gas in liquid mixtures. Compared to a homogeneous BFM (HBFM), the current model includes diffusion coefficients in the momentum transport equations and a field equation for the transport of the gas volume fraction (GVF). Published experimental leakage and dynamic force coefficients for two seals supplied with an air in oil mixture whose GVF varies from 0 (pure liquid) to 20% serve to validate the novel model as well as to benchmark it against predictions from a HBFM. The first seal withstands a large pressure drop (~ 38 bar) and the shaft speed equals 7.5 krpm. The second seal restricts a small pressure drop (1.6 bar) as the shaft turns at 3.5 krpm. The first seal is typical as a balance piston whereas the second seal is found as a neck-ring seal in an impeller. For the high pressure seal and inlet GVF = 0.1, the flow is mostly homogeneous as the maximum diffusion velocity at the seal exit plane is just ~0.1% of the liquid flow velocity. Thus, both the NHBFM and HBFM predict similar flow fields, leakage (mass flow rate) and drag torque. The difference between the predicted leakage and measurement is less than 5%. The NHBFM direct stiffness (K) agrees with the experimental results and reduces faster with inlet GVF than the HBFM K. Both direct damping (C) and cross-coupled stiffness (k) increase with inlet GVF < 0.1.Compared to the test data, the two models generally under predict C and k by ~ 25%. Both models deliver a whirl frequency ratio (fw) ~ 0.3 for the pure liquid seal, hence closely matching the test data. fw raises to ~0.35 as the GVF approaches 0.1. For the low pressure seal the flow is laminar, the experimental results and both NHBFM and HBFM predict a null direct stiffness (K). At an inlet GVF = 0.2, the NHBFM predicted added mass (M) is ~30 % below the experimental result while the HBFM predicts a null M. C and k predicted by both models are within the uncertainty of the experimental results. For operation with either a pure liquid or a mixture (GVF = 0.2), both models deliver fw = 0.5 and equal to the experimental finding. The comparisons of predictions against experimental data demonstrate the NHBFM offers a marked improvement, in particular for the direct stiffness (K). The predictions reveal the fluid flow maintains the homogeneous character known at the inlet condition.

Interactions of brain, blood, and CSF: a novel mathematical model of cerebral edema

Background Previous models of intracranial pressure (ICP) dynamics have not included flow of cerebral interstitial fluid (ISF) and changes in resistance to its flow when brain swelling occurs. We sought to develop a mathematical model that incorporates resistance to the bulk flow of cerebral ISF to better simulate the physiological changes that occur in pathologies in which brain swelling predominates and to assess the model’s ability to depict changes in cerebral physiology associated with cerebral edema. Methods We developed a lumped parameter model which includes a representation of cerebral ISF flow within brain tissue and its interactions with CSF flow and cerebral blood flow (CBF). The model is based on an electrical analog circuit with four intracranial compartments: the (1) subarachnoid space, (2) brain, (3) ventricles, (4) cerebral vasculature and the extracranial spinal thecal sac. We determined changes in pressure and volume within cerebral compartments at steady-state and simulated physiological perturbations including rapid injection of fluid into the intracranial space, hyperventilation, and hypoventilation. We simulated changes in resistance to flow or absorption of CSF and cerebral ISF to model hydrocephalus, cerebral edema, and to simulate disruption of the blood–brain barrier (BBB). Results The model accurately replicates well-accepted features of intracranial physiology including the exponential-like pressure–volume curve with rapid fluid injection, increased ICP pulse pressure with rising ICP, hydrocephalus resulting from increased resistance to CSF outflow, and changes associated with hyperventilation and hypoventilation. Importantly, modeling cerebral edema with increased resistance to cerebral ISF flow mimics key features of brain swelling including elevated ICP, increased brain volume, markedly reduced ventricular volume, and a contracted subarachnoid space. Similarly, a decreased resistance to flow of fluid across the BBB leads to an exponential-like rise in ICP and ventricular collapse. Conclusions The model accurately depicts the complex interactions that occur between pressure, volume, and resistances to flow in the different intracranial compartments under specific pathophysiological conditions. In modelling resistance to bulk flow of cerebral ISF, it may serve as a platform for improved modelling of cerebral edema and blood–brain barrier disruption that occur following brain injury.