Passive Regime Research Articles

Laser operation and Raman self-frequency conversion in Yb:KYW microchip laser

We present a diode-pumped Yb:KYW microchip laser. The passive Q-switchedand CW regimes of operation for the Yb:KYW microchip laser have been investigated. An efficiency for CW operation of up to 10% with regard to incident pump has been obtained. Raman self-frequency conversion in the Q-switched regime has been observed.

Compost convective airflow under passive aeration.

For composting, passive aeration can save energy costs while being just as efficient as forced or active aeration. Passive aeration requires the proper design of aeration ducts, and thus, the proper prediction of the convective airflow rates created by the temperature differential between the compost and the ambient air. To establish such relationship, the temperature and convective air flow regimes of composts were investigated using three bulking agents (wood shavings, hay and straw), each at three moisture contents (MC-60%, 65% and 70%) spanning the normal values. All bulking agent and aeration treatments were aerated in duplicate under passive and active regimes. Laboratory vessels of 105 L were used for all treatments. Passive aeration treatments produced temperatures above 57 degrees C, as did the treatments actively aerated at 4 mg of air s(-1) kg(-1) of initial dry compost material. Compost MC had an effect only on the peak compost temperature, occurring between day 2 and 6. After 6 days of composting, MC no longer had any effect on temperature regime because of the loss of moisture by each mixture. A relationship was established between the Grasholf number (Gr-ratio of buoyancy to viscous forces) and the convective airflow rates, to size the aeration ducts for passive aeration. In general, convective airflow rates ranged from 1.5 to 0.7 mg of dry air s(-1) kg(-1) of initial compost dry matter, from day 0 to day 20, respectively, and for all compost treatments. This airflow rate sizes the aeration ducts installed under compost piles for passive aeration. As compared to straw where airflow rate dropped over a given level of Gr, wood shavings and hay were found to be more effective as bulking agents, as their airflow rate increased constantly with Gr.

Monetary Instrument Problem Revisited: The Role of Fiscal Policy

The monetary instrument problem is examined in an endowment economy model with various stochastic disturbances, with minimizing the variance of inflation as the policy objective. Following current developments in the theory of fiscal determination of the price level, for different monetary policies, active or passive fiscal policy is specified to guarantee a unique equilibrium. The responses of inflation to various structural disturbances in the constant money growth rate-passive fiscal (the active monetary-passive fiscal regime, or the conventional regime where Ricardian equivalence and Quantity Theory of Money hold) and the constant interest rate-active fiscal regime (the passive monetary-active fiscal regime, or the regime where fiscal policy determines the price level) are explained based on monetary and fiscal policies' role in financing government deficit changes and satisfying the government budget constraint in each regime, which is different from the explanations of past research following Poole. One of the interesting findings is that an increase in the steady state real value of nominal government debts (bonds) reduces the variance of inflation in the passive monetary-active fiscal regime.

Corrosion Performance Projection of Yucca Mountain Waste Packages

ABSTRACTThe proposed high-level nuclear waste repository at Yucca Mountain relies heavily on the corrosion resistance of waste packages (WP) emplaced in tunnels bored through tuffaceous rock for adequate performance during the anticipated 10,000 years regulatory period. Present WP design uses a ∼20-mm-thick outer shell of Alloy 22 as the main corrosion-resistant barrier. The operating conditions may include an initial high-temperature (>96 °C) pulse that will last approximately several hundred to a thousand years. Ti-alloy shields are envisioned to prevent water from directly dripping on the WP. However, recent findings suggest that deliquescent salts and other contaminants on the WP surfaces may cause liquid water to form there, even at high temperatures. Current performance projections predict that during the anticipated regulatory period localized corrosion modes will be unlikely and that the Alloy 22 barrier will degrade primarily by very slow uniform dissolution, essentially under passive surface conditions. A review is presented of the assumptions and experimental findings leading to those projections, as well as a discussion of findings of a recent Workshop on the challenges involved in extrapolating limited information on corrosion behavior over an extremely long service period that extends beyond the time frame of common engineering experience. Potential mechanisms for deterioration of the passive regime that may be encountered under those circumstances are discussed.

Chromium-doped LiCAF laser passively Q switched with a V^3+:YAG crystal

A tunable, lamp-pumped Cr3+:LiCaAlF6 laser that operates in the 760-800-nm wavelength range is demonstrated. As a passive Q switch the V3+:YAG crystal, characterized by wide saturable absorption in the 760-900-nm wavelength range, was applied. The V3+:YAG parameters were determined by spectroscopic and saturable transmission measurements. The 30-mJ output energy at 2-Hz repetition rate in the free-running regime was obtained in a cavity reinforced by a diaphragm near the fundamental mode. The dispersive prism inserted into the cavity enabled tuning in the 760-800-nm wavelength range. In the passive Q-switching regime we achieved greater than 1-mJ energy with 50-ns pulse duration in a 35-cm-long cavity. A numerical model that takes into account the short recovery time of V3+:YAG (approximately 5 ns) and excited-state absorption was used to analyze such a laser.

Application of <inline-formula><math display="inline" overflow="scroll"><msup><mstyle mathvariant="normal"><mtext>V</mtext></mstyle><mrow><mi>3+</mi></mrow></msup><mi>:YAG</mi></math></inline-formula> crystals for <bold>Q</bold>-switching and mode-locking of 1.3-μm diode-pumped neodymium lasers

High-power passive Q-switching and mode-locking operation regimes of diode end-pumped Nd:YAG, Nd:YVO 4 , and Nd:YAP active media, operating at a 1.34-μm wavelength are investigated with V 3 + :YAG crystal as the saturable absorber. The highest average power of 2.1 W results from a Nd:YVO 4 crystal placed in a 70-mm-long linear cavity. The corresponding pulse peak power and width are 0.1 kW and 133 ns, respectively. Employing a Nd:YAP crystal and 35-mm cavity length, the highest peak power of ∼2.8 kW results when the laser runs at a 6.5-kHz repetition rate for an average power of ∼0.4 W. A record of 79-μJ pulse energy results from a 64-mm-long resonator with Nd:YAG gain media, however, for a decreased average power of 0.24 W and pulses of 40-ns width. The mode-locking operation regime is investigated in a Z-type cavity. The best results, namely, ∼0.5 W average power with mode-locked envelope energy in excess of 30 μJ and mode-locked pulse energy of 0.7 μJ, are obtained from the Nd:YVO 4 media. Trains of 1-μs-wide pulses with improved stability result from a 1.5-m-long designed cavity with KTP crystal applied for passive negative feedback. A numerical modeling that takes into account the short recovery time of V 3 + :YAG saturable absorber (∼5 ns) and excited state absorption effect is used to analyze and obtain general rules for optimizing such lasers.

Active and passive ocean regimes in a low-order climate model

A system of five ordinary differential equations is studied which combines the Lorenz-84 model for the atmosphere and a box model for the ocean. The behaviour of this system is studied as a function of the coupling parameters. For most parameter values, the dynamics of the atmosphere model is dominant. For a range of parameter values, competing attractors exist. The Kaplan-Yorke dimension and the correlation dimension of the chaotic attractor are numerically calculated and compared to the values found in the uncoupled Lorenz model. In the transition from periodic behaviour to chaos intermittency is observed. The intermittent behaviour occurs near a Neimark-Sacker bifurcation at which a periodic solution loses its stability. The length of the periodic intervals is governed by the time scale of the ocean component. Thus, in this regime the ocean model has a considerable influence on the dynamics of the coupled system.

Polarisation dynamics of monomode Nd 3+:YAG lasers with Cr 4+ saturable absorber: influence of the pump polarisation

Polarisation dynamics has been studied in a monomode Nd 3+:YAG microchip laser with Cr 4+ saturable absorber in the passive Q-switching regime with a linearly polarised pump. The emission is usually linearly polarised and the azimuth of the laser polarisation is shown to depend on the relative orientation of the pump polarisation, the crystalline axis and the direction of the cavity polarisation eigenstates. The laser output intensity and polarisation exhibit qualitatively different dependencies on the azimuth of the pump polarisation when the stress-induced birefringence dominates the saturable loss anisotropy and vice versa. Experimental observations are in agreement with the results of a phase sensitive rate equation model including all these ingredients.

Calculation of Peridotite Partial Melting from Thermodynamic Models of Minerals and Melts, IV. Adiabatic Decompression and the Composition and Mean Properties of Mid-ocean Ridge Basalts

Composition, mean pressure, mean melt fraction, and crustal thickness of model mid-ocean ridge basalts (MORBs) are calculated using MELTS. Polybaric, isentropic batch and fractional melts from ranges in source composition, potential temperature, and final melting pressure are integrated to represent idealized passive and active flow regimes. These MELTS-derived polybaric models are compared with other parameterizations; the results differ both in melt compositions, notably at small melt fractions, and in the solidus curve and melt productivity, as a result of the self-consistent energy balance in MELTS. MELTS predicts a maximum mean melt fraction (~0·08) and a limit to crustal thickness (<=15 km) for passive flow. For melting to the base of the crust, MELTS requires an ~200°C global potential temperature range to explain the range of oceanic crustal thickness; conversely, a global range of 60°C implies conductive cooling to ~50 km. Low near-solidus productivity means that any given crustal thickness requires higher initial pressure in MELTS than in other models. MELTS cannot at present be used to model details of MORB chemistry because of errors in the calibration, particularly Na partitioning. Source heterogeneity cannot explain either global or local Na–Fe systematics or the FeO–K2O/TiO2 correlation but can confound any extent of melting signal in CaO/Al2O3.

Monetary Regimes and the Coordination of Wage Setting

International comparisons show that countries with coordinated wage setting generally have lower unemployment than countries with less coordinated wage setting. This paper argues that the monetary regime may affect whether coordination among many wage setters is feasible. A strict monetary regime, like a country-specific inflation target, to some extent disciplines wage setters, so that the consequences of uncoordinated wage setting are less detrimental than under a more passive monetary regime (e.g., a monetary union). Thus, the gains from coordination are larger under a passive regime. Under some circumstances a passive regime may induce cooperation in wage setting, and thus lower unemployment, when a stricter regime would not.

Active and passive ocean regimes in a low-order climate model

Active and passive ocean regimes in a low-order climate model

Second-harmonic generation by Nd^3+:YAG/Cr^4+:YAG-laser pulses with changing state of polarization

We describe the passive Q-switching regime of a neodymium laser that contains a Cr4+:YAG saturable absorber inside the cavity. Two configurations of the laser cavity are modeled: the cavity containing a partial polarizer as an additional unit and the microchip laser cavity in which the functions of an active element and saturable absorber are combined in a single piece of a Nd3+:YAG/Cr4+:YAG crystal with reflecting facets. It is shown that both lasers are able to generate a giant pulse with a changing state of polarization. Both the kinetics of the state of polarization of the pulse and its impact on second-harmonic generation are treated numerically. We find that the up-conversion efficiency can be enhanced and that harmonic-pulse compression can be obtained by means of the proper orientations of the intracavity polarizing elements, for the first configuration, or by choosing the polarization of the longitudinal pump and angular orientation of the doubling crystal, for the second one. The ability of the doubling crystal to analyze the state of polarization of pulses with nonlinearly changing polarization is discussed.

Investigation of Negative Feedback Regimes for Generation of Compressed Pulses

The results of optimisation of active and passive negative feedback (NF) for generation of stable compressed picosecond pulse trains in Nd:glass and Nd:YAG lasers using a modulator driven by fast photomultiplier and a GaAs passive element are presented. Conditions of prolonged pulse trains generation with the duration of trains varied from 0.3 µs to 200 µs depending on parameters of active NF were investigated. Generation of long (1000 ns) pulse trains in passive NF regime was obtained. Pulse compression in active and passive NF regimes (from 8 ps to 1.4 ps and from 35 ps to 13 ps, respectively) was achieved.

Picosecond semiconductor lasers with an external fibre resonator

The passive mode-locking regime of multisection GaAlAs heterostructure laser diodes has been studied. Pieces of single-mode optical fibres with an edge nonselective mirror or a fibre Bragg grating have been used as an external cavity. Regular trains of optical pulses a few picosecond long and with a peak power of a few watts have been obtained under dc current injection. Spectral characteristics of the pulses are crucially dependent on the parameters and adjustment of the external cavity.

Monetary Regime and the Co-Ordination of Wage Setting

International comparisons show that countries with co-ordinated wage setting generally have lower unemployment than countries with less co-ordinated wage setting. This paper argues that the monetary regime may affect whether co-ordination among many wage setters is feasible. A strict monetary regime, like a country-specific inflation target, to some extent disciplines wage setters, so that the consequences of uncoordinated wage setting are less detrimental than under a more passive monetary regime (eg a monetary union). Thus, the gains from co-ordination are larger under a passive regime. Under some circumstances a passive regime may induce co-operation in wage setting, and thus lower unemployment, when a stricter regime would not.

High-temperature oxidation behavior of SiC-coated carbon fiber-reinforced carbon matrix composites

Abstract The high-temperature oxidation behavior of bare and SiC-coated carbon fiber-reinforced carbon matrix (C/C) composites was examined in the temperature range 900–3000 K. In the course of the measurements, the main focus was placed upon the effect of oxygen partial pressure on the oxidation behavior and the transition temperature between the passive and active oxidation regimes. To understand the oxidation behavior of SiC-coated C/C composites quantitatively, a morphological characterization of coating cracks was carried out, and then, in the oxygen diffusion controlling temperature range, an analytical model was developed for the prediction of weight loss due to oxidation of SiC-coated C/C composites. The oxidation rates derived from this model were in fairly good agreement with the experiment results.

From active to passive oxidation: O 2 on Si(111) 7×7

The interaction of oxygen with the Si(111) 7×7 surface was studied by in situ real-time experiments in a high-temperature scanning tunneling microscope at temperatures between 350 and 600°C for oxygen partial pressures of 10 −8 to 10 −7 mbar during an exposure ranging from 0 to 200 L. The early adsorption stage (0–2 L) is dominated by the occurrence of dark adatom states. There are also small numbers of various other features such as bright and grey states which are partially reversible or show random walk behaviour. In the transition region between active and passive oxidation regimes (500–600°C, 10 −8–10 −7 mbar) we observe etching of step edges and holes and simultaneously homogeneous or heterogeneous oxide nucleation at surface defects with further lateral oxide growth affecting the next Si layer after terrace retraction. This competition leads to a rather rough surface morphology where the step edges are locally pinned by the oxide. The oxidation reaction towards the passive regime is characterized by the formation of a homogeneous thin oxide (passivating film) on the entire surface without indications for an island growth mode from where further oxide growth proceeds slowly. From the temperature dependence of the step-flow mode etch rate in the active regime, we determine an activation energy of (1.6±0.2) eV which is comparable to the step edge detachment energy of atoms required for annealing of oxygen-induced vacancies on the terraces.

Cyclical passive stretch influences the mechanical properties of the inactive cat soleus.

The effects of cyclical, passive manipulation (PM, 30 min day(-1), 5 days week(-1) for 6 months) mimicking the length excursions observed during stepping on the mechanical and associated biochemical properties of the inactive cat soleus muscle were determined in five cats. Inactivity was produced via spinal cord isolation (SI), i.e. complete spinal cord transections at low thoracic and high sacral levels and bilateral dorsal rhizotomy between the transection sites. Passive manipulation was administered to one leg of each SI cat. Compared with normal controls, SI resulted in approximately 70% decrease in weight, an 80% decrease in maximum tetanic tension (Po) and an approximately 100% increase in maximum rate of shortening (Vmax) and myosin adenosine triphosphatase (mATPase) activity of the soleus. The passive manipulation regime partially ameliorated these effects. When compared with the control SI soleus, the SI-PM soleus weight and maximum tetanic tension were 12 and 21% higher, respectively, and the Vmax and mATPase activity 21 and 12% (p > 0.05) lower, respectively. Thus, inactivity resulted in a smaller and faster muscle, whereas passive manipulation for only 30 min a day tended to maintain these properties closer to normal control values. The results suggest a potential therapeutic effect of short bouts of cyclical, passive manipulation on otherwise inactive skeletal muscles.

Mid-Ocean Ridge Melting: Constraints from Lithospheric Xenoliths at Oahu, Hawaii

One plagioclase–spinel lherzolite and four spinel lherzolite xenoliths from Oahu, Hawaii, contain clinopyroxene grains that show homogeneous rare earth element (REE) abundances and smooth REE patterns with systematic depletion of light REE (LREE). These five xenoliths are mid-ocean ridge basalt (MORB) magma-depleted residues with compositions that were not modified by later metasomatism. Trace element systematics of these xenoliths were used to investigate the melt production rate (dF/dP) within a 90-my-old residual mantle column (RMC). Such rates were calculated as ratios of the difference in extents of depletion (dF) to the difference in equilibrium pressures (dP) between two xenolith samples. The extents of melting were modeled from REE, Sr and Zr abundances in clinopyroxene; and equilibrium pressures were inferred from the two-pyroxene geobarometer of Mercier et al. (1984, Contributions to Mineralogy and Petrology, 85, 391–403). Equilibrium pressures range from 21 to 7 kbar and extents of melting vary from 2 to 8%. Together, these data constrain the maximum extent of melting in the garnet lherzolite stability field to be <2% and a dF/dP of 0.43%/kbar within the stability field of spinel lherzolite. Uncertainties in the estimates of equilibrium pressure and extent of depletion lead to a slightly broader range of dF/dP values (0.26-0.78%/kbar). These values are significantly lower than that of ∼1.2%/kbar suggested by most previous studies. With the best estimated mean dF/dP of 0.43%/kbar, only 3.9 km of crust could have been generated by melting lherzolite in the pressure range of 26–7 kbar. The thickness and composition of the crust that overlies the 90 Ma Oahu RMC require a higher extent of melting. Based on the REE abundances, most samples from the 90 Ma crust and East Pacific Rise can be explained as pooled melts derived from the lherzolitic source in a passive melting regime with a maximum extent of melting (Fmax) of 30%. This model produces a dF/dP of 4.4%/kbar in the pressure range of 7–2 kbar and generates an additional 1.8 km of crust. In detail, the high [Sm/Yb]DM ratios in most East Pacific Rise samples cannot be explained by melting a lherzolitic source. Instead, they reflect mixing between two components: (1) the pooled melt derived from lherzolitic source in a passive melting regime with an Fmax of 30% (∼80% of the mixture) and (2) melt derived from garnet pyroxenite by 40% fractional melting (∼20% of the mixture). This model produces 7.1 km of crust.

Mid-Ocean Ridge Melting: Constraints from Lithospheric Xenoliths at Oahu, Hawaii

by melting a lherzolitic source. Instead, they reflect mixing between One plagioclase–spinel lherzolite and four spinel lherzolite xenoliths two components: (1) the pooled melt derived from lherzolitic source from Oahu, Hawaii, contain clinopyroxene grains that show homoin a passive melting regime with an Fmax of 30% (~80% of the geneous rare earth element (REE) abundances and smooth REE mixture) and (2) melt derived from garnet pyroxenite by 40% patterns with systematic depletion of light REE (LREE). These fractional melting (~20% of the mixture). This model produces five xenoliths are mid-ocean ridge basalt (MORB) magma-depleted 7·1 km of crust. residues with compositions that were not modified by later metasomatism. Trace element systematics of these xenoliths were used to investigate the melt production rate (dF/dP) within a 90-my-old residual mantle column (RMC). Such rates were calculated as