scholarly journals CH<sub>4</sub> exchange at the forest floor of a forestry-drained fen: low flux rates but high temporal variation

2016 ◽  
Author(s):  
Mika Korkiakoski ◽  
Markku Koskinen ◽  
Kari Minkkinen ◽  
Paavo Ojanen ◽  
Timo Penttilä ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Linear Regression ◽  
Exchange Rates ◽  
Measurement System ◽  
Forest Floor ◽  
Steel Frames ◽  
Tree Stand ◽  
Ch4 Flux ◽  
Exponential Regression ◽  
Moss Layer

Abstract. We measured methane (CH4) exchange rates with automatic chambers at the forest floor of a nutrient-rich drained peatland in 2011–2013. The fen, located in southern Finland, was drained for forestry in the 1970s and the tree stand is now a mixture of Scots pine, Norway spruce and pubescent birch. Our measurement system consisted of six transparent polycarbonate chambers and stainless steel frames, positioned on a number of different field and moss layer types. Flux rates were calculated with both linear and exponential regression. The use of linear regression systematically underestimated CH4 flux rates by 20–50 % when compared to exponential regression. However, the use of exponential regression with small fluxes (

scholarly journals Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes

2017 ◽  
Vol 14 (7) ◽  
pp. 1947-1967 ◽  
Author(s):  
Mika Korkiakoski ◽  
Juha-Pekka Tuovinen ◽  
Mika Aurela ◽  
Markku Koskinen ◽  
Kari Minkkinen ◽  
...  
Keyword(s):  
Linear Regression ◽  
Forest Floor ◽  
Early Summer ◽  
Late Winter ◽  
Exponential Regression ◽  
Biological Phenomena ◽  
Moss Layer ◽  
Dry Conditions ◽  
Ch4 Uptake ◽  
Heavy Rainfall Events

Abstract. We measured methane (CH4) exchange rates with automatic chambers at the forest floor of a nutrient-rich drained peatland in 2011–2013. The fen, located in southern Finland, was drained for forestry in 1969 and the tree stand is now a mixture of Scots pine, Norway spruce, and pubescent birch. Our measurement system consisted of six transparent chambers and stainless steel frames, positioned on a number of different field and moss layer compositions. Gas concentrations were measured with an online cavity ring-down spectroscopy gas analyzer. Fluxes were calculated with both linear and exponential regression. The use of linear regression resulted in systematically smaller CH4 fluxes by 10–45 % as compared to exponential regression. However, the use of exponential regression with small fluxes ( <  2.5 µg CH4 m−2 h−1) typically resulted in anomalously large absolute fluxes and high hour-to-hour deviations. Therefore, we recommend that fluxes are initially calculated with linear regression to determine the threshold for low fluxes and that higher fluxes are then recalculated using exponential regression. The exponential flux was clearly affected by the length of the fitting period when this period was  <  190 s, but stabilized with longer periods. Thus, we also recommend the use of a fitting period of several minutes to stabilize the results and decrease the flux detection limit. There were clear seasonal dynamics in the CH4 flux: the forest floor acted as a CH4 sink particularly from early summer until the end of the year, while in late winter the flux was very small and fluctuated around zero. However, the magnitude of fluxes was relatively small throughout the year, ranging mainly from −130 to +100 µg CH4 m−2 h−1. CH4 emission peaks were observed occasionally, mostly in summer during heavy rainfall events. Diurnal variation, showing a lower CH4 uptake rate during the daytime, was observed in all of the chambers, mainly in the summer and late spring, particularly in dry conditions. It was attributed more to changes in wind speed than air or soil temperature, which suggest that physical rather than biological phenomena are responsible for the observed variation. The annual net CH4 exchange varied from −104 ± 30 to −505 ± 39 mg CH4 m−2 yr−1 among the six chambers, with an average of −219 mg CH4 m−2 yr−1 over the 2-year measurement period.

scholarly journals CO<sub>2</sub> flux determination by closed-chamber methods can be seriously biased by inappropriate application of linear regression

2007 ◽  
Vol 4 (6) ◽  
pp. 1005-1025 ◽  
Author(s):  
L. Kutzbach ◽  
J. Schneider ◽  
T. Sachs ◽  
M. Giebels ◽  
H. Nykänen ◽  
...  
Keyword(s):  
Linear Regression ◽  
Nonlinear Regression ◽  
Co2 Flux ◽  
Exponential Model ◽  
Co2 Uptake ◽  
Co2 Fluxes ◽  
Closed Chamber ◽  
Exponential Regression ◽  
Closure Time ◽  
Over Time

Abstract. Closed (non-steady state) chambers are widely used for quantifying carbon dioxide (CO2) fluxes between soils or low-stature canopies and the atmosphere. It is well recognised that covering a soil or vegetation by a closed chamber inherently disturbs the natural CO2 fluxes by altering the concentration gradients between the soil, the vegetation and the overlying air. Thus, the driving factors of CO2 fluxes are not constant during the closed chamber experiment, and no linear increase or decrease of CO2 concentration over time within the chamber headspace can be expected. Nevertheless, linear regression has been applied for calculating CO2 fluxes in many recent, partly influential, studies. This approach has been justified by keeping the closure time short and assuming the concentration change over time to be in the linear range. Here, we test if the application of linear regression is really appropriate for estimating CO2 fluxes using closed chambers over short closure times and if the application of nonlinear regression is necessary. We developed a nonlinear exponential regression model from diffusion and photosynthesis theory. This exponential model was tested with four different datasets of CO2 flux measurements (total number: 1764) conducted at three peatlands sites in Finland and a tundra site in Siberia. Thorough analyses of residuals demonstrated that linear regression was frequently not appropriate for the determination of CO2 fluxes by closed-chamber methods, even if closure times were kept short. The developed exponential model was well suited for nonlinear regression of the concentration over time c(t) evolution in the chamber headspace and estimation of the initial CO2 fluxes at closure time for the majority of experiments. However, a rather large percentage of the exponential regression functions showed curvatures not consistent with the theoretical model which is considered to be caused by violations of the underlying model assumptions. Especially the effects of turbulence and pressure disturbances by the chamber deployment are suspected to have caused unexplainable curvatures. CO2 flux estimates by linear regression can be as low as 40% of the flux estimates of exponential regression for closure times of only two minutes. The degree of underestimation increased with increasing CO2 flux strength and was dependent on soil and vegetation conditions which can disturb not only the quantitative but also the qualitative evaluation of CO2 flux dynamics. The underestimation effect by linear regression was observed to be different for CO2 uptake and release situations which can lead to stronger bias in the daily, seasonal and annual CO2 balances than in the individual fluxes. To avoid serious bias of CO2 flux estimates based on closed chamber experiments, we suggest further tests using published datasets and recommend the use of nonlinear regression models for future closed chamber studies.

scholarly journals Effects of bracket design on critical contact angle

2013 ◽  
Vol 83 (5) ◽  
pp. 877-884 ◽  
Author(s):  
Xiaomo Liu ◽  
Peng Ding ◽  
Jiuxiang Lin
Keyword(s):  
Contact Angle ◽  
Stainless Steel ◽  
Linear Regression ◽  
Resistance To Sliding ◽  
The Relationship ◽  
State Resistance ◽  
Critical Contact ◽  
Bracket Design

ABSTRACT Objective: To explore how the position of the bracket slots relative to the archwire influences the friction between them, and how bracket design affects the critical contact angle (θc). Materials and Methods: Two kinds of stainless steel archwires (0.016 and 0.019 × 0.025-inch) were tested against four kinds of brackets (Transmission Straight Archwire bracket, Domestic MBT bracket, Tip-Edge Plus bracket, and BioQuick self-ligation bracket) in the dry state. Resistance to sliding (RS) was measured as an increase in contact angle (θ). The value of θc was calculated by two linear regression lines. Results: Friction remained stable when θ &lt; θc, then increased linearly when θ &gt; θc. The θc values of the Tip-Edge Plus bracket and Transmission Straight Archwire bracket were significantly larger than those for the Domestic MBT bracket and BioQuick self-ligation bracket. Conclusions: The relationship between the archwire and bracket slot significantly affects the resistance to sliding. The “edge-off” structure of the Tip-Edge Plus bracket and Transmission Straight Archwire bracket could help to increase the θc value, and to expand the passive configuration range.

Analysis of Eddy-Current Measurement System for Residual Stress Assessment in Stainless Steel Grade 304

2015 ◽  
Vol 659 ◽  
pp. 623-627 ◽  
Author(s):  
Cherdpong Jomdecha ◽  
Isaratat Phung-On
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Eddy Current ◽  
Measurement System ◽  
System Analysis ◽  
Stress Measurement ◽  
Steel Grade ◽  
Current Measurement ◽  
Residual Stress Measurement ◽  
Stress Assessment

The objective of this paper is an analysis of statistical discreteness and measurement capability of an eddy-current measurement system for residual stress assessment in stainless steel Grade 304 (SS304). Cylindrical specimens with 50 mm in diameter and 12 mm thickness were prepared to generate residual stress by Resistance Spot Welding at which the welding currents were set at 12, 14, and 16 kA. The eddy-current measurement system was including a probe with frequency range of 0.1 to 3 MHz and an eddy current flaw detector. They were performed by contacting the probe on the specimen. The measurements were performed particularly in the vicinity of heat affected zone (HAZ). In order to determine the results of the residual stress measurement, the calibration curves between static tensile stress and eddy current impedance at various frequencies were accomplished. The Measurement System Analysis (MSA) was utilized to evaluate the changed eddy-current probe impedance from residual stress. The results showed that using eddy current technique at 1 MHz for residual stress measurement was the most efficient. It can be achieved the Gauge Repeatability & Reproducibility %GR&R at 16.61479 and Number of Distinct Categories (NDC) at 8. As applied on actual butt welded joint, it could yield the uncertainty of ± 58 MPa at 95 % (UISO).

scholarly journals The Effect of Exchange Value on the Stock Index Listed in Indonesia Stock Exchange during Covid-19 Pandemic

2021 ◽  
Vol 2 (1) ◽  
pp. 6-14
Author(s):  
Zahra Zhafira ◽  
Einde Evana ◽  
Ratna Septiyanti
Keyword(s):  
Regression Analysis ◽  
Exchange Rate ◽  
Linear Regression ◽  
Exchange Rates ◽  
Stock Exchange ◽  
Linear Regression Analysis ◽  
Stock Index ◽  
Simple Linear Regression ◽  
Simple Linear Regression Analysis ◽  
Stock Indices

This study aims to examine the effect of exchange rates on the stock index during the Covid-19 pandemic. This research was conducted using secondary data. The population in this study were all stock indices listed on the Indonesia Stock Exchange with a sample size of 89 and a total stock index of 34. The study period was 4 months, 17 January 2020 to 20 May 2020. The sample data collection of this study used the purposive method. Sampling with world economic conditions and Indonesia which are weakening due to the Covid-19 pandemic and based on the phenomenon that the exchange rate is experiencing a continuous movement even every year the exchange rate depreciates IDR against the US Dollar. One of the causes of the high fluctuation of the rupiah exchange rate against the dollar came from economic factors such as inflation, the interest rate on Bank Indonesia certificates during the Covid-19 pandemic. This study uses a simple linear regression analysis method using SPSS V.26. The results of simple linear regression analysis show that exchange rates have a negative and significant effect on all stock indices listed on the Indonesia Stock Exchange, these results have similarities or differences with the results of research in other emerging market countries.

scholarly journals Hubungan Kecepatan Pendinginan Air dengan Kecepatan Tiupan Udara

2017 ◽  
Vol 2 ◽  
pp. 241
Author(s):  
Taat Guswantoro ◽  
Manogari Sianturi ◽  
Nurafni Prapitasari ◽  
Areli Elona
Keyword(s):  
Regression Analysis ◽  
Wind Speed ◽  
Linear Regression ◽  
Water Temperature ◽  
Rate Of Change ◽  
Hot Water ◽  
Water Cooling ◽  
Exponential Regression ◽  
The Relationship

<p class="AbstractEnglish"><strong>Abstract</strong>: In this study hot water was placed in two erlenmeyer scale 100 ml clogged and without plug, each filled with 150 ml hot water and allowed to cool in air. Measurement of water temperature using sensor connected to the interface and recorded using the pasco capstone 14.1. The wind is raised with the fan, to adjust the wind speed by adjusting the fan distance, the speed is measured using an anemometer. The water cooling constant is obtained by a decay exponential regression analysis of temperature vs time. The relationship between water colling coefficient with wind speed is used linear regression. From the research, the water cooling coefficient naturally for clogging erlenmeyer is 3,1 x 10<sup>-4</sup> s<sup>-1</sup> and for erlenmeyer without plug 3.8 x 10<sup>-4</sup> s<sup>-1</sup>, the rate of change of water cooling constant to wind speed is 1 , 4 x 10<sup>-4</sup> m<sup>-1</sup>.</p><p class="KeywordsEngish"> </p><p class="AbstrakIndonesia"><strong>Abstrak: </strong>Pada penelitian ini air panas ditempatkan dalam dua buah erlenmeyer berskala 100 ml bersumbat dan tanpa sumbat, masing-masing diisi air panas dengan volume 150 ml dan dibiarkan mendingin di udara. Pengukuran suhu air dengan menggunakan sensor panas yang dihubungkan ke interface dan dicatat menggunakan program pasco capstone 14.1. Angin dibangkitkan dengan kipas, untuk mengatur kecepatan angin dengan cara mengatur jarak kipas, kecepatan angin diukur menggunakan anemometer. Konstanta pendinginan air diperoleh dengan analisis regresi eksponensial meluruh dari data suhu dan waktu. Hubungan antara koefisien pendinginan air dengan kecepatan angin digunakan regresi linier. Dari penelitian diperoleh koefisien pendinginan air secara alami untuk erlenmeyer tersumbat sebesar 3,1 x 10<sup>-4</sup> s<sup>-1</sup> dan untuk erlenmeyer tanpa sumbat sebesar  3,8 x 10<sup>-4</sup> s<sup>-1</sup>, laju perubahan konstanta pendinginan air terhadap kecepatan angin adalah sebesar 1,4 x 10<sup>-4</sup> m<sup>-1</sup><sub>.</sub></p>

Influence of geometric and material nonlinearities on the behaviour and design of stainless steel frames

2021 ◽  
Vol 187 ◽  
pp. 106981
Author(s):  
F. Walport ◽  
I. Arrayago ◽  
L. Gardner ◽  
D.A. Nethercot
Keyword(s):  
Stainless Steel ◽  
Steel Frames
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