An NMR protocol for determining ice crystal size distributions during freezing and pore size distributions during freeze-drying

1999 ◽  
Vol 17 (4) ◽  
pp. 537-556 ◽  
Author(s):  
J. Godward ◽  
P. Gunning ◽  
B. P. Hills
Keyword(s):  
Pore Size ◽  
Freeze Drying ◽  
Crystal Size ◽  
Size Distributions ◽  
Ice Crystal ◽  
Crystal Size Distributions ◽  
Pore Size Distributions ◽  
Ice Crystal Size

scholarly journals Supersaturation Variability and Cirrus Ice Crystal Size Distributions

2014 ◽  
Vol 71 (8) ◽  
pp. 2905-2926 ◽  
Author(s):  
B. Kärcher ◽  
A. Dörnbrack ◽  
I. Sölch
Keyword(s):  
Crystal Size ◽  
Ice Crystals ◽  
Future Research ◽  
Small Scale ◽  
Size Distributions ◽  
Ice Crystal ◽  
Tropical Tropopause ◽  
Crystal Size Distributions ◽  
Mass Fluxes ◽  
Ice Crystal Size

Abstract Small-scale dynamical variability affects atmospheric supersaturation and therefore the development of ice clouds via uptake of water vapor on ice crystals. This variability and its implications for ice growth are difficult to capture experimentally and theoretically. By interpreting supersaturation as a stochastic variable, the authors examine the average temporal behavior of, and the link between, supersaturation fluctuations and ice crystal size distributions in upper-tropospheric cirrus clouds. The authors classify cirrus types according to their ability to dampen supersaturation fluctuations owing to depositional growth of cloud ice and study how size distributions in them respond to supersaturation variability, investigating the possibility of the occurrence of ice-supersaturated states within cirrus. Typical time scales for growth and damping impacts on supersaturation are minutes and minutes to hours, respectively, and are highly variable among cirrus types and within single clouds. Transient deviations from saturated equilibrium states can occur depending on the ice crystal number concentration and size and on the strength of the small-scale dynamical forcing. Supersaturation preferentially occurs in cloud regions with few small ice crystals. The authors demonstrate that supersaturation fluctuations in very thin tropical tropopause cirrus create long-lived supersaturated states. Furthermore, they potentially generate few large ice crystals, broadening size distributions, and significantly enhance water mass fluxes due to sedimentation. Although not studied here, they may also allow new ice crystals to nucleate. Implications of these findings for those clouds to dehydrate air entering the lower stratosphere are discussed and future research needs are outlined.

scholarly journals An Assessment of the Impact of Antishattering Tips and Artifact Removal Techniques on Cloud Ice Size Distributions Measured by the 2D Cloud Probe

2014 ◽  
Vol 31 (12) ◽  
pp. 2567-2590 ◽  
Author(s):  
Robert C. Jackson ◽  
Greg M. McFarquhar ◽  
Jeff Stith ◽  
Matthew Beals ◽  
Raymond A. Shaw ◽  
...  
Keyword(s):  
Crystal Size ◽  
National Research Council ◽  
Ice Crystals ◽  
Size Distributions ◽  
Ice Crystal ◽  
Considerable Uncertainty ◽  
Crystal Size Distributions ◽  
Ice Crystal Size ◽  
Cloud Ice ◽  
The Impact

Abstract Prior estimates of ice crystal size distributions derived from 2D cloud probes (2DCs) have been artificially amplified by small ice crystals generated from the shattering of large ice crystals on the probe tips. Although antishatter tips and algorithms exist, there is considerable uncertainty in their effectiveness. This paper examines differences in ice crystal size distributions from adjacent 2DCs with standard and antishatter tips, and processed with and without antishattering algorithms. The measurements were obtained from the National Research Council of Canada Convair-580 during the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) and the National Center for Atmospheric Research C-130 during the 2011 Instrumentation Development and Education in Airborne Science (IDEAS-2011). The 2DC size distributions are compared with those from the Holographic Detector for Clouds (HOLODEC), which has antishatter tips and allows for identification of shattering through spatial statistics. The ratio of the number concentration N of particles with maximum dimensions 125–500 μm from the 2DC with standard tips to that from the 2DC with modified tips was correlated with median mass diameter and perimeter divided by area, but not with airspeed, attack, and attitude angles. Antishatter tips and algorithms reduced N by up to a factor of 10 for IDEAS-2011 and ISDAC, but neither alone removed all artifacts. For the period with coincident data, both N from the HOLODEC and 2DC with modified tips are around 5 × 10−3 L−1 μm−1, suggesting that antishatter tips and algorithms combined remove artifacts from the 2DC for the conditions sampled during IDEAS-2011.

scholarly journals Determination of Ice Crystal Size Distributions in Frozen Desserts

1991 ◽  
Vol 74 (10) ◽  
pp. 3334-3344 ◽  
Author(s):  
D.P. Donhowe ◽  
R.W. Hartel ◽  
R.L. Bradley
Keyword(s):  
Crystal Size ◽  
Size Distributions ◽  
Ice Crystal ◽  
Crystal Size Distributions ◽  
Ice Crystal Size

scholarly journals The influence of freezing rates on bovine pericardium tissue Freeze-drying

2009 ◽  
Vol 52 (6) ◽  
pp. 1493-1504 ◽  
Author(s):  
Camila Figueiredo Borgognoni ◽  
Virgilio Tattini Junior ◽  
Ana Maria Irene Bartolomeu Ayrosa ◽  
Bronislaw Polakiewicz ◽  
Adolfo Alberto Leirner ◽  
...  
Keyword(s):  
Freeze Drying ◽  
Heart Valves ◽  
Crystal Size ◽  
Initial Step ◽  
Bovine Pericardium ◽  
Ice Crystal ◽  
Structural Behaviour ◽  
Drying Time ◽  
Secondary Drying ◽  
Ice Crystal Size

The bovine pericardium has been used as biomaterial in developing bioprostheses. Freeze-drying is a drying process that could be used for heart valve's preservation. The maintenance of the characteristics of the biomaterial is important for a good heart valve performance. This paper describes the initial step in the development of a bovine pericardium tissue freeze-drying to be used in heart valves. Freeze-drying involves three steps: freezing, primary drying and secondary drying. The freezing step influences the ice crystal size and, consequently, the primary and secondary drying stages. The aim of this work was to investigate the influence of freezing rates on the bovine pericardium tissue freeze-drying parameters. The glass transition temperature and the structural behaviour of the lyophilized tissues were determined as also primary and secondary drying time. The slow freezing with thermal treatment presented better results than the other freeze-drying protocols.

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