The proton, one of the components of atomic nuclei, is composed of fundamental particles called quarks and gluons. Gluons are the carriers of the force that binds quarks together, and free quarks are ...never found in isolation-that is, they are confined within the composite particles in which they reside. The origin of quark confinement is one of the most important questions in modern particle and nuclear physics because confinement is at the core of what makes the proton a stable particle and thus provides stability to the Universe. The internal quark structure of the proton is revealed by deeply virtual Compton scattering
, a process in which electrons are scattered off quarks inside the protons, which subsequently emit high-energy photons, which are detected in coincidence with the scattered electrons and recoil protons. Here we report a measurement of the pressure distribution experienced by the quarks in the proton. We find a strong repulsive pressure near the centre of the proton (up to 0.6 femtometres) and a binding pressure at greater distances. The average peak pressure near the centre is about 10
pascals, which exceeds the pressure estimated for the most densely packed known objects in the Universe, neutron stars
. This work opens up a new area of research on the fundamental gravitational properties of protons, neutrons and nuclei, which can provide access to their physical radii, the internal shear forces acting on the quarks and their pressure distributions.
The physics of the gravitational form factors of the proton, as well as their understanding within quantum chromodynamics, has advanced significantly in the past two decades through both theory and ...experiment. This Colloquium provides an overview of this progress, highlights the physical insights unveiled by studies of gravitational form factors, and reviews their interpretation in terms of the mechanical properties of the proton.
I give an overview on experimental studies of the spectrum and the structure of the excited states of the nucleon and what we can learn about their in ternal structure. One focus is on the efforts to ...obtain a more complete picture of the light-quark baryon exci tation spectrum employing electromagnetic beams that will allow us to draw some conclusions on the symme tries underlying the spectrum. For the higher mass ex citations, the full employment of coupled channel ap proaches is essential when searching for new excited states in the large amounts of data already accumulated in different channels involving a variety of polarization observables. The other focus is on the study of transition form factors and helicity amplitudes and their de pendences on
Q
2
, especially on some of the more promi nent resonances, especially Δ(1232)3/2
+
,
N
(1440)1/2
+
, and negative parity states
N
(1535)1/2
-
, and
N
(1675)5/2
-
.These were obtained in pion and eta electroproduction experi ments off proton targets and have already led to further insights in the active degrees-of-freedom as a function of the distance scale involved.
Elastic electron-proton scattering (e-p) and the spectroscopy of hydrogen atoms are the two methods traditionally used to determine the proton charge radius, r
. In 2010, a new method using muonic ...hydrogen atoms
found a substantial discrepancy compared with previous results
, which became known as the 'proton radius puzzle'. Despite experimental and theoretical efforts, the puzzle remains unresolved. In fact, there is a discrepancy between the two most recent spectroscopic measurements conducted on ordinary hydrogen
. Here we report on the proton charge radius experiment at Jefferson Laboratory (PRad), a high-precision e-p experiment that was established after the discrepancy was identified. We used a magnetic-spectrometer-free method along with a windowless hydrogen gas target, which overcame several limitations of previous e-p experiments and enabled measurements at very small forward-scattering angles. Our result, r
= 0.831 ± 0.007
± 0.012
femtometres, is smaller than the most recent high-precision e-p measurement
and 2.7 standard deviations smaller than the average of all e-p experimental results
. The smaller r
we have now measured supports the value found by two previous muonic hydrogen experiments
. In addition, our finding agrees with the revised value (announced in 2019) for the Rydberg constant
-one of the most accurately evaluated fundamental constants in physics.
Review of Particle Physics Barnett, R M; Beringer, J; Dahl, O ...
Progress of theoretical and experimental physics,
2020, Letnik:
2020, Številka:
8
Journal Article
Recenzirano
Odprti dostop
Abstract
The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 3,324 new measurements from 878 papers, we list, evaluate, and average measured ...properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 120 reviews are many that are new or heavily revised, including a new review on High Energy Soft QCD and Diffraction and one on the Determination of CKM Angles from B Hadrons.
The Review is divided into two volumes. Volume 1 includes the Summary Tables and 98 review articles. Volume 2 consists of the Particle Listings and contains also 22 reviews that address specific aspects of the data presented in the Listings.
The complete Review (both volumes) is published online on the website of the Particle Data Group (pdg.lbl.gov) and in a journal. Volume 1 is available in print as the PDG Book. A Particle Physics Booklet with the Summary Tables and essential tables, figures, and equations from selected review articles is available in print and as a web version optimized for use on phones as well as an Android app.
•Haematococcus pluvialis is one of the major natural sources of astaxanthin.•Astaxanthin is a powerful antioxidant that acts in the combat of free radicals.•The enzymatic lysis is promising for the ...recovery of astaxanthin from H. pluvialis.•The precipitation pressure had influence on the particle size formed.•SEDS encapsulation efficiency of 51.21% was achieved.
In this work, the effectiveness of different enzymatic techniques for cell wall disruption of Haematococcus pluvialis for the extraction of carotenoids and subsequent encapsulation of extracts in the co-polymer poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) using the Solution Enhanced Dispersion by Supercritical fluids (SEDS) technique was investigated. Glucanex® performed best compared with Lyticase® and Driselase®. The conditions for enzymatic lysis using this enzyme preparation were established as a pH of 4.5, a temperature of 55°C, an initial activity of β-1,3-glucanase of 0.6UmL−1 and a reaction time of 30min. Enzymatic lysis assisted by ultrasound without biomass freezing was shown to be a promising and simple one-step technique for cell wall disruption, reaching 83.90% extractability. In the co-precipitation experiments, the highest encapsulation efficiency (51.21%) was obtained when using a higher biomass to dichloromethane ratio (10mgmL−1) at the carotenoid extraction step and a lower pressure of precipitation (80bar). In these conditions, spherical particles in the micrometer range (0.228μm) were obtained.
In this work, 12 different yeast strains were evaluated to gauge their ability to accumulate lipids using raw glycerol as the main carbon source.
Lipomyces lipofer
NRRL Y-1155 stood out above the ...other strains, achieving 9.48 g/l biomass, 57.64 % lipid content and 5.46 g/l lipid production. The fatty acid profile was similar to vegetable oils commonly used in the synthesis of biodiesel, with the predominance of polyunsaturated acids, especially linoleic acid, reaching 68.3 % for
Rhodotorula glutinis
NRRL YB-252. The occurrence of palmitic acid (39.3 % for
Lipomyces starkeyi
NRRL Y-11557) was also notable. Thus, yeast biomass with high lipid content can be a sustainable and renewable alternative as a raw material for the biodiesel industry.
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