39 research outputs found
Laser-induced bound-state phases in high-order harmonic generation
We present single-molecule and macroscopic calculations showing that
laser-induced Stark shifts contribute significantly to the phase of high-order
harmonics from polar molecules. This is important for orbital tomography, where
phases of field-free dipole matrix elements are needed in order to reconstruct
molecular orbitals. We derive an analytical expression that allows the
first-order Stark phase to be subtracted from experimental measurements
Polarization effects in attosecond photoelectron spectroscopy
We study the influence of polarization effects in streaking by combined atto-
and femtosecond pulses. The polarization-induced terms alter the streaking
spectrum. The normal streaking spectrum, which maps to the vector potential of
the femtosecond pulse, is modified by a contribution following the field
instead. We show that polarization effects may lead to an apparent temporal
shift, that needs to be properly accounted for in the analysis. The effect may
be isolated and studied by angle-resolved photoelectron spectroscopy from
oriented polar molecules. We also show that polarization effects will lead to
an apparent temporal shift of 50 as between photoelectrons from a 2p and 1s
state in atomic hydrogen.Comment: 4 pages, 3 figure
Vibrational excitation of diatomic molecular ions in strong-field ionization of diatomic molecules
A model based on the strong-field and Born-Oppenheimer approximations
qualitatively describes the distribution over vibrational states formed in a
diatomic molecular ion following ionization of the neutral molecule by intense
laser pulses. Good agreement is found with a recent experiment [X. Urbain et
al., Phys. Rev. Lett. 92, 163004 (2004)]. In particular, the observed deviation
from a Franck-Condon-like distribution is reproduced. Additionally, we
demonstrate control of the vibrational distribution by a variation of the peak
intensity or a change of frequency of the laser pulse.Comment: 4 pages, 4 figure
Two-center minima in harmonic spectra from aligned polar molecules
We extend a model of two-center interference to include the superposition of
opposite orientations in aligned polar molecules. We show that the position of
the minimum in the harmonic spectrum from both aligned and oriented CO depends
strongly on the relative recombination strength at different atoms, not just
the relative phase. We reinterpret the minimum in aligned CO as an interference
between opposite orientations, and obtain good agreement with numerical
calculations. Inclusion of the first-order Stark effect shifts the position of
the interference minimum in aligned CO even though aligned molecules do not
posses total permanent dipoles. We explain the shift in terms of an extra phase
that the continuum electron of oriented CO accumulates due to the Stark effect
Influence of molecular symmetry on strong-field ionization: Studies on ethylene, benzene, fluorobenzene, and chlorofluorobenzene
Using the molecular strong-field approximation we consider the effects of
molecular symmetry on the ionization of molecules by a strong, linearly
polarized laser pulse. Electron angular distributions and total ionization
yields are calculated as a function of the relative orientation between the
molecule and the laser polarization. Our studies focus on ethylene
(CH), benzene (CH), fluorobenzene (CHF), and ortho
chlorofluorobenzene (1,2 CHClF), the molecules representing four
different point groups. The results are compared with experiments, when
available, and with the molecular tunneling theory appropriately extended to
non-linear polyatomic molecules. Our investigations show that the orientational
dependence of ionization yields is primarily determined by the nodal surface
structure of the molecular orbitals.Comment: 13 pages, 10 figures. Submitted to Physical Review
Research of combustion in older generation spark-ignition engines in the condition of use leaded and unleaded petrol
This paper analyzes the potential problems in the exploitation of the older generation of spark-ignition engines with higher octane number of petrol (unleaded petrol BMB 95) than required (leaded petrol MB 86). Within the experimental tests on two different engines (STEYR-PUCH model 712 and GAZ 41) by applying piezoelectric pressure sensors integrated with the engine spark plugs, acceleration sensors and special electronic block connected with distributor, show that the cumulative first and second theoretical phase of combustion when petrol of higher octane number (BMB 95) is used lasts slightly longer than when the low-octane petrol MB 86 is used. For new petrol (BMB 95) higher optimal angles of pre-ignition have been determined by which better performances of the engine are achieved without a danger of the combustion with detonation (also called knocking)
Research of combustion in older generation spark-ignition engines in the condition of use leaded and unleaded petrol
This paper analyzes the potential problems in the exploitation of the older generation of spark-ignition engines with higher octane number of petrol (unleaded petrol BMB 95) than required (leaded petrol MB 86). Within the experimental tests on two different engines (STEYR-PUCH model 712 and GAZ 41) by applying piezoelectric pressure sensors integrated with the engine spark plugs, acceleration sensors and special electronic block connected with distributor, show that the cumulative first and second theoretical phase of combustion when petrol of higher octane number (BMB 95) is used lasts slightly longer than when the low-octane petrol MB 86 is used. For new petrol (BMB 95) higher optimal angles of pre-ignition have been determined by which better performances of the engine are achieved without a danger of the combustion with detonation (also called knocking)
From ultraslow to extremely fast dynamics in sodium nitrate
Increasing dynamics in solids featuring nuclei subjected to second-order quadrupolar interactions lead to central-transition spectra that undergo two consecutive line-shaped transitions. Conventional motional narrowing occurs when the molecular exchange rate is on the order of the strength of the dominant interaction. In a second step, the resulting intermediately narrowed spectra change further when the motion becomes faster than the Larmor precession rate, leading to terminally narrowed spectra that can display a residual quadrupolar shift. We derive analytic expressions for this shift and analyze the quadrupolar central-transition spectra in terms of CN symmetrical cone models. Increasing the number of sites to N ≥ 3, the terminally narrowed spectra remain unaltered, while the intermediately narrowed spectra remain unaltered only for N ≥ 5. This finding relates to the different (cubic vs. icosahedral) symmetries that are required to average out the spatial second- and fourth-rank terms in the second-order quadrupolar interaction. Following recent work (Hung et al., Solid State Nucl Magn Reson 84:14–19, 2017), 17O NMR is applied to examine the three-site rotation of the nitrate group in NaNO3. Line shapes are measured and analyzed, and in addition to prior work, satellite-transition and stimulated-echo experiments are carried out. The final-state amplitudes extracted from the latter are reproduced using model calculations. It is shown how two-dimensional exchange spectra relating to N-site cone motions can be decomposed in terms of effective two-site-jump spectra. This latter approach is successfully tested for NaNO3
Research of combustion in older generation spark-ignition engines in the condition of use leaded and unleaded petrol
This paper analyzes the potential problems in the exploitation of the older
generation of spark-ignition engines with higher octane number of petrol
(unleaded petrol BMB 95) than required (leaded petrol MB 86). Within the
experimental tests on two different engines (STEYR-PUCH model 712 and GAZ 41)
by applying piezoelectric pressure sensors integrated with the engine spark
plugs, acceleration sensors (accelerometers) and special electronic block
connected with distributor, show that the cumulative first and second
theoretical phase of combustion when petrol of higher octane number (BMB 95)
is used lasts slightly longer than when the low-octane petrol MB 86 is used.
For new petrol (BMB 95) higher optimal angles of pre-ignition have been
determined by which better performances of the engine are achieved without a
danger of the combustion with detonation (also called knocking)
Inhibition of the ATP Synthase Eliminates the Intrinsic Resistance of Staphylococcus aureus towards Polymyxins
Staphylococcus aureus is intrinsically resistant to polymyxins (polymyxin B and colistin), an important class of cationic antimicrobial peptides used in treatment of Gram-negative bacterial infections. To understand the mechanisms underlying intrinsic polymyxin resistance in S. aureus, we screened the Nebraska Transposon Mutant Library established in S. aureus strain JE2 for increased susceptibility to polymyxin B. Nineteen mutants displayed at least 2-fold reductions in MIC, while the greatest reductions (8-fold) were observed for mutants with inactivation of either graS, graR, vraF, or vraG or the subunits of the ATP synthase (atpA, atpB, atpG, or atpH), which during respiration is the main source of energy. Inactivation of atpA also conferred hypersusceptibility to colistin and the aminoglycoside gentamicin, whereas susceptibilities to nisin, gallidermin, bacitracin, vancomycin, ciprofloxacin, linezolid, daptomycin, and oxacillin were unchanged. ATP synthase activity is known to be inhibited by oligomycin A, and the presence of this compound increased polymyxin B-mediated killing of S. aureus. Our results demonstrate that the ATP synthase contributes to intrinsic resistance of S. aureus towards polymyxins and that inhibition of the ATP synthase sensitizes S. aureus to this group of compounds. These findings show that by modulation of bacterial metabolism, new classes of antibiotics may show efficacy against pathogens towards which they were previously considered inapplicable. In light of the need for new treatment options for infections with serious pathogens like S. aureus, this approach may pave the way for novel applications of existing antibiotics