ALBERT

Description: This paper presents a design methodology of multisine signals, so that they can be used as phase references or standards convenient for modulated measurements. To achieve an extendable measurement bandwidth, the spectrum of each multisine is designed with three successive segments, where the left (lower-frequency) and right (higher-frequency) ending ones have the same phase spectra. In this way several multisines, one by one overlapped at the ending segments, can jointly serve as an integrated phase reference/standard signal, which in theory has an arbitrarily extendable bandwidth. By the example of “Schroeder” phase relationship, the proposed method is experimentally verified for wideband modulated measurements, where the designed multisines are used as the phase references and standards, respectively, of a nonlinear vector network analyzer test bed. In this work, a phase measurement error less than ±1 deg. is experimentally confirmed for 1601-tone measurements with 160 MHz modulation bandwidth around 2 GHz.

Description: Central Asia is currently a semiarid-arid region, dominated by the Westerlies. It is important to understand mechanisms of climate and precipitation changes here, as water availability in the region is crucial today and in the future. High-resolution, absolutely-dated oxygen isotope (δ18O) records of stalagmites from Kesang Cave characterize a dynamic precipitation history over most of the past 500,000 years. This record demonstrates, for the first time, that climate change in the region exhibits a processional rhythm with abrupt inceptions of low δ18O speleothem growth at times of high Northern Hemisphere summer insolation followed by gradual δ18O increases that track decreases of insolation. These observations and interpretations contrast with the interpretation of nearby, but higher elevation ice core records. The absolutely-dated cave δ18O shifts can be used to correlate the regional climate variability by providing chronological marks. Combined with other paleoclimate records, the Kesang observations suggest that possible incursions of Asian summer monsoon rainfall or related moisture into the Kesang site and/or adjacent areas during the high insolation times may play an important role in changing orbital-scale hydrology of the region. Based on our record, arid climate will prevail in this region for the next several millennia, providing that anthropogenic effects do not supersede natural processes.

Description: The bi-spectral method retrieves cloud optical thickness ( τ ) and cloud droplet effective radius ( r e ) simultaneously from a pair of cloud reflectance observations, one in a visible or near infrared (VIS/NIR) band and the other in a shortwave-infrared (SWIR) band. A cloudy pixel is usually assumed to be horizontally homogeneous in the retrieval. Ignoring sub-pixel variations of cloud reflectances can lead to a significant bias in the retrieved τ and r e . In the literature, the retrievals of τ and r e are often assumed to be independent and considered separately when investigating the impact of sub-pixel cloud reflectance variations on the bi-spectral method. As a result, the impact on τ is contributed only by the sub-pixel variation of VIS/NIR band reflectance and the impact on r e only by the sub-pixel variation of SWIR band reflectance. In our new framework, we use the Taylor expansion of a two-variable function to understand and quantify the impacts of sub-pixel variances of VIS/NIR and SWIR cloud reflectances and their covariance on the τ and r e retrievals. This framework takes into account the fact that the retrievals are determined by both VIS/NIR and SWIR band observations in a mutually dependent way. In comparison with previous studies, it provides a more comprehensive understanding of how sub-pixel cloud reflectance variations impact the τ and r e retrievals based on the bi-spectral method. In particular, our framework provides a mathematical explanation of how the sub-pixel variation in VIS/NIR band influences the r e retrieval and why it can sometimes outweigh the influence of variations in the SWIR band and dominate the error in r e retrievals, leading to a potential contribution of positive bias to the r e retrieval. We test our framework using synthetic cloud fields from a large-eddy simulation and real observations from MODIS. The predicted results based on our framework agree very well with the numerical simulations. Our framework can be used to estimate the retrieval uncertainty from sub-pixel reflectance variations in operational satellite cloud products and to help understand the differences in τ and r e retrievals between two instruments.

Description: High-pressure (HP) metagreywacke from the Namche Barwa complex, Eastern Himalayan Syntaxis (EHS), consists of garnet, biotite, plagioclase, quartz, rutile and ilmenite with or without K-feldspar, sillimanite, cordierite, spinel and orthopyroxene. Two types of metagreywacke are recognized: medium-temperature (MT) and high-temperature (HT) types. Garnet in the MT metagreywacke shows significant growth zoning and contains lower MgO than the weakly zoned garnet in the HT metagreywacke. Petrographic observations and phase equilibria modelling for four representative samples indicate that both types of metagreywacke experienced clockwise P–T paths subdivided into three stages: stage I is the pre-peak prograde to pressure peak ( P max ) stage characterized by progressive increase in P–T conditions. The P max conditions are estimated using the garnet composition with maximum CaO, being 12.5–13.5 kbar and 685–725 °C for the MT metagreywacke, and 15–16 kbar and 825–835 °C for the HT one. Stage II is the post- P max decompression with heating or near-isothermal to T max stage and the T max conditions, constrained using the garnet compositions with maximum MgO, are 11 kbar and 760 °C for the MT metagreywacke, and ~12 kbar and 830–845 °C for the HT one. The modelled mineral assemblages at T max are garnet + biotite + K-feldspar + rutile + plagioclase ± ilmenite in the presence of melt for both types of metagreywacke, consistent with the petrographic observations. Stage III is the post- T max retrograde metamorphism, characterized by decompression and cooling. The modelling suggests that the melts with high Na/K ratios (1.7–5.2) have been produced during stages I and II, which could be responsible for the formation of sodium-rich leucogranites. This study and previous results indicate that the Higher Himalayan Crystallines (HHC) in the Eastern Himalayan Syntaxis consist of MT–HP and HT–HP metamorphic units separated by a speculated tectonic contact. Petrological and structural discontinuities within the EHS cannot be easily interpreted with ‘tectonic aneurysm’ model. This article is protected by copyright. All rights reserved.

Description: A continuous countercurrent supercritical CO 2 extraction-distillation dual-column process was developed to extract and concentrate natural vitamin E (VE) from soybean oil deodorizer distillate (SODD). The experimental results demonstrated that process parameters such as extraction pressure, temperature, and solvent-to-feed ratio significantly impacted on the extraction efficiency of natural VE. A new five-parameter mass transfer model for the continuous countercurrent supercritical CO 2 extraction-distillation dual-column process was presented based on the Penetration and Double-Film theories. The calculated values of the mathematical model agreed well with the experimental data, with absolute average relative deviation values of less than 25 %. A continuous countercurrent supercritical CO 2 extraction-distillation dual-column process was developed to extract and concentrate natural vitamin E from soybean oil deodorizer distillate. A new five-parameter mass transfer model for this process was presented based on the Penetration and Double-Film theories.

Description: Soot oxidation with NO (in the absence of gas phase O 2 ) on potassium-supported Mg-Al hydrotalcite mixed oxides (K/MgAlO) was studied using a temperature-programmed reaction and in situ FTIR techniques. Nitrite and the ketene group were identified as the reaction intermediates and thus a nitrite-ketene mechanism was proposed in which surface active oxygen on K sites of K/MgAlO is transferred to soot by NO through nitrites. In the absence of gas phase O 2 , soot oxidation with NO at lower temperatures (below 450 °C) is limited by the amount of active oxygen on the K sites. This kind of active oxygen is not reusable but can be replenished in the presence of gas phase O 2 . Soot oxidation with NO on K/MgAIO was studied by temperature-programmed reaction and in situ FTIR. The nitrite and the ketene group were identified as the reaction intermediates and thus a nitrite–ketene mechanism was proposed, in which surface active oxygen on K sites is transferred to soot by NO through nitrites, forming the ketene group.

Description: The Levant constitutes an important region for assessing linkages between climate and societal changes throughout the course of human history. However, large uncertainties remain in our understanding of the region's hydroclimate variability under varying boundary conditions. Here we present a new high-resolution, precisely-dated speleothem oxygen-carbon isotope and Sr/Ca records, spanning the last 20ka from Jeita Cave, northern Levant. Our record reveals a higher (lower) precipitation-evaporation (P-E) balance during the Last Glacial Maximum and Bølling interstadial (Heinrich stadial 1). The early-mid Holocene is characterized by a trend towards higher P-E state, culminating between ~7 and 6 ka BP. The mid-late Holocene is characterized by two millennial-length drier periods during 5.3–4.2 and 2.8–1.4ka BP. On sub-millennial scale, the northern Levant climate variability is dominated by 500-year periodicity. Comparisons with the regional proxy records suggest persistent out-of-phase climate variability between the northern and southern Levant on a wide-range of timescales.

Description: We present the results of three-dimensional, nonhydrostatic simulations of internal tides and waves in the South China Sea (SCS) using the SUNTANS model. Model results accurately predict the observed wave arrival times at two mooring locations in the SCS. Internal wave amplitudes are underpredicted which causes underprediction of internal wave speeds due to a lack of amplitude dispersion. We show that the well-known A and B waves arise from the steepening of semidiurnal internal tides that are generated due to strong barotropic flow over ridges in the Luzon Strait. A wave generation is stronger in the southern portion of the Luzon Strait because diurnal internal tidal beams augment the amplitude of the semidiurnal A waves. B wave generation is stronger in the northern portion where the distance between the eastern and western ridges is approximately equal to one internal tidal wavelength and leads to semidiurnal internal tidal resonance. The orientation of the ridges produces large A waves that propagate into the northern portion of the western SCS basin and stronger B waves that propagate into the southern portion. When traced back in time along linear characteristics, A waves consistently line up close to peak ebb (eastward) barotropic currents, while B waves consistently line up with peak flood (westward) barotropic currents. This reinforces the notion that the lee wave mechanism and associated hydraulic or nonlinear effects are weak, as demonstrated by a simple linear model relating the amplitude of the simulated waves to the excursion parameter at the ridges.

Description: Surface ozone (O3), carbon monoxide (CO), and total and speciated reactive nitrogen compounds (NOy, NO, NO2, PAN, HNO3, and particulate NO3−) were measured at Mount Waliguan (WLG; 36.28°N, 100.90°E, 3816 m above sea level (asl)) in the summer of 2006 to further understand the sources of ozone and reactive nitrogen and to investigate the partitioning of reactive nitrogen over the remote Qinghai-Tibetan Plateau. The mean mixing ratios of O3, CO, NOy, and daytime NO were 59 ppbv, 149 ppbv, 1.44 ppbv, and 71 pptv, respectively, which (except for NOy) were higher than those measured from a previous campaign in summer 2003, which is consistent with more frequent transport of anthropogenic pollution from central and eastern China in the measurement period of 2006 (55%) than that of 2003 (25%). The abnormally high values of NOy observed in 2003 were suspected to be due to the positive interference from ammonia (NH3) to the particular catalytic converter used in that study. Varied diurnal patterns were observed for the various NOy components. The ozone production efficiencies (ΔO3/ΔNOz), which were estimated from the slope of the O3-NOz scatterplot, were 7.7–11.3 for the polluted plumes from central and eastern China. The speciation of reactive nitrogen was investigated for the first time in the remote free troposphere in western China. PAN and particulate NO3− were the most abundant reactive nitrogen species at WLG, with average proportions of 32% and 31%, followed by NOx (24%) and HNO3 (20%). The relatively large contribution of particulate NO3− to NOy was due to the presence of high concentrations of NH3 and crustal particles, which favor the formation of particulate nitrate. An analysis of backward trajectories for the recent 10 years revealed that air masses from central and eastern China dominated the airflow at WLG in summer, suggesting strong impact of anthropogenic forcing on the surface ozone and other trace constituents on the Plateau.

Description: Teleseismic receiver function analysis of data from six dense arrays in the western U.S. is used to investigate mantle transition zone (MTZ) discontinuities and the prevalence of a low-velocity layer atop the 410 km discontinuity (410-LVL). Negative polarity Ps arrivals indicative of a low-velocity layer with a top 25–60 km above the 410 are identified in 8–11 out of 18 stacks of receiver functions from highly sampled back azimuth corridors. The 410-LVL is interpreted as partial melt resulting from upwelling of hydrated mantle across a water solubility contrast at the 410. The 669 km mean depth of the 660 km discontinuity (660) and the magnitude of 660 topography suggest variable hydration, locally approaching saturation, in addition to 〉150 K lateral temperature variations beneath five arrays. Mean amplitudes of P410s and P660s increase monotonically with period from 2 to 10 s; however, greater variations are observed in the frequency dependence of P410s compared to P660s implying 410 thickness is more heterogeneous. Variable 410 thickness is attributed to changes in hydration modulating the width of the olivine-to-wadsleyite transition interval. Frequency dependence of P660s amplitudes suggests a broad velocity gradient consistent with multivariate phase changes in the olivine and garnet systems. Sporadic detection of the 410-LVL, the magnitude and length scales of MTZ discontinuity topography, and inferred variations in hydration support the occurrence of vigorous small-scale convection in the western U.S. mantle. Comparison of receiver functions with body wave tomography suggests small-scale convection driven by sinking slab segments and lithospheric instabilities contributes to the intermittent nature of the 410-LVL.