Clocking Enhanced Ionization of Hydrogen Molecules with Rotational Wave Packets.

Laser-induced rotational wave packets of H_{2} and D_{2} molecules were experimentally measured in real time by using two sequential 25-fs laser pulses and a reaction microscope. By measuring the time-dependent yields of the above-threshold dissociation and the enhanced ionization of the molecule, we observed a few-femtosecond time delay between the two dissociation channels for both H_{2} and D_{2}. The delay was interpreted and reproduced by a classical model that considers enhanced ionization and thus additional interaction within the laser pulse. We demonstrate that by accurately measuring the phase of the rotational wave packet in hydrogen molecules we can resolve dissociation dynamics which is occurring within a fraction of a molecular rotation. Such a rotational clock is a general concept applicable to sequential fragmentation processes in other molecules.

Experimental Evidence for Quantum Tunneling Time.

The first hundred attoseconds of the electron dynamics during strong field tunneling ionization are investigated. We quantify theoretically how the electron's classical trajectories in the continuum emerge from the tunneling process and test the results with those achieved in parallel from attoclock measurements. An especially high sensitivity on the tunneling barrier is accomplished here by comparing the momentum distributions of two atomic species of slightly deviating atomic potentials (argon and krypton) being ionized under absolutely identical conditions with near-infrared laser pulses (1300 nm). The agreement between experiment and theory provides clear evidence for a nonzero tunneling time delay and a nonvanishing longitudinal momentum of the electron at the "tunnel exit."

Electron-Nuclear Coupling through Autoionizing States after Strong-Field Excitation of H_{2} Molecules.

Channel-selective electron emission from strong-field photoionization of H_{2} molecules is experimentally investigated by using ultrashort laser pulses and a reaction microscope. The electron momenta and energy spectra in coincidence with bound and dissociative ionization channels are compared. Surprisingly, we observed an enhancement of the photoelectron yield in the low-energy region for the bound ionization channel. By further investigation of asymmetrical electron emission using two-color laser pulses, this enhancement is understood as the population of the autoionizing states of H_{2} molecules in which vibrational energy is transferred to electronic energy. This general mechanism provides access to the vibrational-state distribution of molecular ions produced in a strong-field interaction.

Attosecond tracing of correlated electron-emission in non-sequential double ionization.

Despite their broad implications for phenomena such as molecular bonding or chemical reactions, our knowledge of multi-electron dynamics is limited and their theoretical modelling remains a most difficult task. From the experimental side, it is highly desirable to study the dynamical evolution and interaction of the electrons over the relevant timescales, which extend into the attosecond regime. Here we use near-single-cycle laser pulses with well-defined electric field evolution to confine the double ionization of argon atoms to a single laser cycle. The measured two-electron momentum spectra, which substantially differ from spectra recorded in all previous experiments using longer pulses, allow us to trace the correlated emission of the two electrons on sub-femtosecond timescales. The experimental results, which are discussed in terms of a semiclassical model, provide strong constraints for the development of theories and lead us to revise common assumptions about the mechanism that governs double ionization.

Association between timing of intensive care unit admission and outcomes for emergency department patients with community-acquired pneumonia.

OBJECTIVE: To compare the 28-day mortality and hospital length of stay of patients with community-acquired pneumonia who were transferred to an intensive care unit on the same day of emergency department presentation (direct-transfer patients) with those subsequently transferred within 3 days of presentation (delayed-transfer patients). DESIGN: Secondary analysis of the original data from two North American and two European prospective, multicenter, cohort studies of adult patients with community-acquired pneumonia. PATIENTS: In all, 453 non-institutionalized patients transferred within 3 days of emergency department presentation to an intensive care unit were included in the analysis. Supplementary analysis was restricted to patients without an obvious indication for immediate transfer to an intensive care unit. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The sample consisted of 138 delayed-transfer and 315 direct-transfer patients, among whom 150 (33.1%) were considered to have an obvious indication for immediate intensive care unit admission. After adjusting for the quintile of propensity score, delayed intensive care unit transfer was associated with an increased odds ratio for 28-day mortality (2.07; 95% confidence interval, 1.12-3.85) and a decreased odds ratio for discharge from hospital for survivors (0.53; 95% confidence interval, 0.39-0.71). In a propensity-matched analysis, delayed-transfer patients had a higher 28-day mortality rate (23.4% vs. 11.7%; p = 0.02) and a longer median hospital length of stay (13 days vs. 7 days; p < .001) than direct-transfer patients. Similar results were found after excluding the 150 patients with an obvious indication for immediate intensive care unit admission. CONCLUSIONS: Our findings suggest that some patients without major criteria for severe community-acquired pneumonia, according to the recent Infectious Diseases Society of America/American Thoracic Society consensus guideline, may benefit from direct transfer to the intensive care unit. Further studies are needed to prospectively identify patients who may benefit from direct intensive care unit admission despite a lack of major severity criteria for community-acquired pneumonia based on the current guidelines.

Risk stratification of early admission to the intensive care unit of patients with no major criteria of severe community-acquired pneumonia: development of an international prediction rule.

INTRODUCTION: To identify risk factors for early (< three days) intensive care unit (ICU) admission of patients hospitalised with community-acquired pneumonia (CAP) and not requiring immediate ICU admission, and to stratify the risk of ICU admission on days 1 to 3. METHODS: Using the original data from four North American and European prospective multicentre cohort studies of patients with CAP, we derived and validated a prediction rule for ICU admission on days 1 to 3 of emergency department (ED) presentation, for patients presenting with no obvious reason for immediate ICU admission (not requiring immediate respiratory or circulatory support). RESULTS: A total of 6560 patients were included (4593 and 1967 in the derivation and validation cohort, respectively), 303 (4.6%) of whom were admitted to an ICU on days 1 to 3. The Risk of Early Admission to ICU index (REA-ICU index) comprised 11 criteria independently associated with ICU admission: male gender, age younger than 80 years, comorbid conditions, respiratory rate of 30 breaths/minute or higher, heart rate of 125 beats/minute or higher, multilobar infiltrate or pleural effusion, white blood cell count less than 3 or 20 G/L or above, hypoxaemia (oxygen saturation < 90% or arterial partial pressure of oxygen (PaO2) < 60 mmHg), blood urea nitrogen of 11 mmol/L or higher, pH less than 7.35 and sodium less than 130 mEq/L. The REA-ICU index stratified patients into four risk classes with a risk of ICU admission on days 1 to 3 ranging from 0.7 to 31%. The area under the curve was 0.81 (95% confidence interval (CI) = 0.78 to 0.83) in the overall population. CONCLUSIONS: The REA-ICU index accurately stratifies the risk of ICU admission on days 1 to 3 for patients presenting to the ED with CAP and no obvious indication for immediate ICU admission and therefore may assist orientation decisions.