The thickness of monolayers is a fundamental property of two-dimensional (2D) materials that has not found the necessary attention. It plays a crucial role in their mechanical behavior, the ...determination of related physical properties such as heat transfer, and especially the properties of multilayer systems. Measurements of the thickness of free-standing monolayers are widely lacking and notoriously too large. Consistent thicknesses have been reported for single layers of graphene, boronitrene, and SiC derived from interlayer spacing measured by X-ray diffraction in multilayer systems, first-principles calculations of the interlayer spacing, and tabulated van der Waals (vdW) diameters. Furthermore, the electron density-based volume model agrees with the geometric slab model for graphene and boronitrene. For other single-atom monolayers DFT calculations and molecular dynamics (MD) simulations deliver interlayer distances that are often much smaller than the vdW diameter, owing to further electrostatic and (weak) covalent interlayer interaction. Monolayers strongly bonded to a surface also show this effect. If only weak vdW forces exist, the vdW diameter delivers a reasonable thickness not only for free-standing monolayers but also for few-layer systems and adsorbed monolayers. Adding the usually known corrugation effect of buckled or puckered monolayers to the vdW diameter delivers an upper limit of the monolayer thickness. The study presents a reference database of thickness values for elemental and binary group-IV and group-V monolayers, as well as binary III-V and IV-VI compounds.
The thickness of monolayers is a fundamental property of two-dimensional (2D) materials that has not found the necessary attention. Since the boundary is not well-defined and it changes its value with the surrounding, the thickness is difficult to grasp.
A review of several classical, algebraic models in nuclear structure physics, which use symmetries as an important tool, are presented. After a conceptual introduction to group theory, a selection of ...models is chosen to illustrate the methods and the power of the usage of symmetries. This enables us to describe very involved systems in a greatly simplified manner. Some problems are also discussed, when ignoring basic principles of nature, such as the Pauli exclusion principle. We also show that occasionally one can rescue these omissions. In a couple of representative models, applications of symmetries are explicitly applied in order to illustrate how extremely complicated systems can be treated. This contribution is meant as a review of the use of algebraic models in nuclear physics, leading to a better understanding of the articles in the same special volume.
A brief review on algebraic extensions of general relativity is presented. After a short summary of first attempts by Max Born and Albert Einstein, all possible algebraic extensions will be ...discussed, with the pseudo‐complex (pc) extension left as the only viable one, because it does not contain ghost solutions. Also some metric extensions are presented, such as the non‐symmetric gravitation theory and the Finsler metric. Some predictions of the pc extension are discussed, such as the structure of light emission of an accretion disk around a black hole, the redshift at the surface of a compact star as a function in the azimuthal angle, and whether there is an upper limit for the mass of a neutron star.
Evidence is reviewed that national economic performance generally has been better under Democrat presidents. It is likely, but not necessarily true, however, that better economic performance is ...related to greater fiscal responsibility. A brief history of federal budget deficits and the gross federal debt for the last seven decades is followed by discussion of why federal budget deficits matter. A simple model is estimated where the shares of federal budget deficits in gross domestic products over the 72-year period from 1950 to 2021 are regressed on the civilian unemployment rate, indicating the state of the economy, and controlling for whether a Democrat or Republican is president and for years the U.S. was engaged in war. An Index of Fiscal Discipline is then regressed on the growth rate in real gross domestic product, again controlling for the party in the White House and war years. The results show that Democrat presidents have been significantly more fiscally responsible.
Abstract
Western North American fires have been increasing in magnitude and severity over the last few decades. The complex coupling of fires with the atmospheric energy budget and meteorology ...creates short-term feedbacks on regional weather altering the amount of pollution to which Americans are exposed. Using a combination of model simulations and observations, this study shows that the severe fires in the summer of 2017 increased atmospheric aerosol concentrations leading to a cooling of the air at the surface, reductions in sensible heat fluxes, and a lowering of the planetary boundary layer height over land. This combination of lower-boundary layer height and increased aerosol pollution from the fires reduces air quality. We estimate that from start of August to end of October 2017, ∼400 premature deaths occurred within the western US as a result of short-term exposure to elevated PM
2.5
from fire smoke. As North America confronts a warming climate with more fires the short-term climate and pollution impacts of increased fire activity should be assessed within policy aimed to minimize impacts of climate change on society.
CASTNET (Clean Air Status and Trends Network) ozone and temperature data and large‐scale meteorological analysis are used to quantify the extent to which meteorological events and their persistence ...impact ozone with an emphasis on the high end of the ozone distribution (greater than the 90th percentile). Ozone increases with each successive stagnation day in all regions of the U.S., with the highest increase in the Northeastern U.S. (0.4 standard deviation or ∼4.7 ppb per successive stagnation day). Ozone increases with days since cyclone passage only in the Northeastern and Mid‐Atlantic regions of the U.S., but on average not enough to reach the 90th percentile concentration. Persistent high temperature does not result in further ozone increases in any region. On the interannual timescale there is little evidence that summers with large numbers of the above events increase ozone preferentially on the high end of the ozone distribution.
Key Points
Ozone increases following successive stagnation days in all four regions of the U.S. examined, increasing by 4.7 ppb d‐1 in the Northeast
Ozone increases with days since cyclone passage in the Northeast and Mid‐Atlantic regions, but generally not to the 90th percentile level
Summers that are hot, have less cyclones, or more stagnation do not have ozone increases preferentially on the high end of the distribution
The co-occurrence of heat waves and pollution events and the resulting high
mortality rates emphasize the importance of the co-occurrence of pollution
and temperature extremes. Through the use of ...extreme value theory and other
statistical methods, tropospheric surface ozone and temperature extremes and
their joint occurrence are analyzed over the United States during the summer
months (JJA) using measurements and simulations of the present and future
climate and chemistry. Five simulations from the Chemistry-Climate Model
Initiative (CCMI) reference experiment using specified dynamics (REFC1SD)
were analyzed: the CESM1 CAM4-chem, CHASER, CMAM, MOCAGE and MRI-ESM1r1
simulations. In addition, a 25-year present-day simulation branched off the
CCMI REFC2 simulation in the year 2000 and a 25-year future simulation
branched off the CCMI REFC2 simulation in 2100 were analyzed using CESM1
CAM4-chem. The last two simulations differed in their concentration of carbon
dioxide (representative of the years 2000 and 2100) but were otherwise
identical. In general, regions with relatively high ozone extremes over the
US do not occur in regions of relatively high temperature extremes. A new
metric, the spectral density, is developed to measure the joint extremal
dependence of ozone and temperature by evaluating the spectral dependence of
their extremes. While in many areas of the country ozone and temperature are
highly correlated overall, the correlation is significantly reduced when
examined on the higher end of the distributions. Measures of spectral density
are less than about 0.35 everywhere, suggesting that at most only about a
third of the time do extreme temperatures coincide with extreme ozone. Two
regions of the US have the strongest measured extreme dependence of ozone and
temperature: the northeast and the southeast. The simulated future increase
in temperature and ozone is primarily due to a shift in their distributions,
not to an increase in their extremes. The locations where the right-hand side
of the temperature distribution does increase (by up to 30 %) are
consistent with locations where soil–moisture feedback may be expected.
Future changes in the right-hand side of the ozone distribution range
regionally between +20 % and −10 %. The location of future increases
in the high-end tail of the ozone distribution are weakly related to those of
temperature with a correlation of 0.3. However, the regions where the
temperature extremes increase are not located where the extremes in ozone are
large, suggesting a muted ozone response.
After resuming some main predictions of the pseudo‐complex General Relativity (pcGR), the effects of a minimal length, on the structure near the event horizon of a Schwarzschild and Kerr black hole, ...are investigated within the pcGR. It is shown that for small mass black holes there are strong effects, for example, avoiding the accumulation of mass, which might be important in the formation of primordial black holes during the Big Bang. The pcGR adds to the metric a contribution characterized by a parameter α$$ \alpha $$, which has a critical value at which barely an event horizon exists. For macroscopic black holes, these effects vanished for below and above this critical value, but at the critical value effects still persist up to m=10−13$$ m={10}^{-13} $$ cm, though quickly disappearing. For very large mass black holes the minimal length can be safely neglected. The limit between a small and a macroscopic black hole, in units of length, is between 10−15$$ {10}^{-15} $$ cm and 10−13$$ {10}^{-13} $$ cm.
There is increased evidence that stratosphere‐troposphere exchange (STE) of ozone has a significant impact on tropospheric chemistry and radiation. Traditional diagnostics of STE consider the ozone ...budget in the lowermost stratosphere (LMS) as a whole. However, this can only render the hemispherically integrated ozone flux and therefore does not distinguish the exchange of ozone into low latitudes from that into high latitudes. The exchange of ozone at different latitudes may have different tropospheric impacts. This present study extends the traditional approach from the entire LMS to individual isentropic layers in the LMS and therefore gives the meridional distribution of STE by the latitudes where each isentropic surface intersects the tropopause. The specified dynamics version of the Whole Atmosphere Community Climate Model is used to estimate the STE ozone flux on each isentropic surface. It is found that net troposphere‐to‐stratosphere ozone transport occurs in low latitudes along the 350–380 K isentropic surfaces and that net stratosphere‐to‐troposphere ozone transport takes place in the extratropics along the 280–350 K isentropes. Particularly, the seasonal cycle of extratropical STE ozone flux in the Northern Hemisphere displays a maximum in late spring and early summer, following the seasonal migration of the upper tropospheric jet and associated isentropic mixing. Furthermore, differential diabatic heating and isentropic mixing tend to induce STE ozone fluxes in opposite directions, but the net effect results in a spatiotemporal pattern similar to the STE ozone flux associated with isentropic mixing.
Key Points
An isentropic diagnostics gives the meridional distribution of stratosphere‐troposphere exchange
The meridional structure of cross‐tropopause ozone flux has a strong connection with the jet
Diabatic heating (mixing) contributes to an upward (downward) cross‐tropopause ozone flux
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